Chapter 5

[W]Vol. I. p. 51.

If these are animals, why have they not all life? why are they in the most fluid part of the liquor alive, while those in the thickest are not so? Leeawenhoek did not perceive that the thick matter, the origin of which he attributes to the humour of the animalculæ, is nothing but a mucilaginous matter which produces them. By diluting this mucilage with water, he would have given life to the whole of them. Even this mucilage is oftentimes only a mass of those bodies which are set in motion on being separated; and consequently this thick matter, instead of being a humour, produced by the animalcules, is only the substance of the animals themselves, or rather, as we have already observed, the matter from which they originate. Speaking of the seed of a cock, Leeuwenhoek says, in his letterto Grew, "Contemplando materiam (seminalem) animadverti ibidem tantam abundantiam viventium animalium, ut ea stuperem; forma seu externa figura sua nostrates anguillas fluviatiles referebant, vehementissima agitatione movebantur; quibus tamen substrati videbantur multi & admodum exiles globuli, item multæ plan-ovales figuræ, quibus etiam vita posset attribui, & quidem propter earundem commotiones; sed existimabam omnes hasce commotiones & agitationes pro venire ab animalcules, sicque etiam res se habebat; attamen ego non opinione solum, sed etiam ad veritatem mihi persuadeo has particulas planam & ovalem figuram habentes, esse quædam animalcula inter se ordine suo disposita & mixta vitaque adhuc carentia." Here we see in the same seminal liquor animalcules of different forms; and I am convinced, by my own experiments, that if Leeuwenhoek had closely observed these oval substances, he would have discovered that they moved by their own powers, and that consequently they were as much alive as the rest. This change perfectly coincides with what I have said, that they are organic particles which take different forms, and not constant species of animals; for in the presentcase, if the bodies, which have the figure of an eel, are true spermatic animalcules, each, destined to become a cock, which supposes a very perfect organization, and a very constant form, what will those be which have an oval figure, and what end do they answer? He says indeed afterwards, that these ovals maybe conceived to be the same animals, by supposing their bodies to be twisted in a spiral form; but then how shall we conceive that an animal, whose body is constrained, can move without being extended? I maintain, therefore, that these oval substances are no other than the organic particles separated from their threads, and that the eels were the separated parts which dragged those threads after them, as I have many times perceived in other seminal liquors.

Leeuwenhoek, who imagined all these moving bodies were animals, and established a system thereon; who also pretended, that spermatic animals must become men and animals, now suspected they were only natural machines, or organic particles in motion; for he does not doubt these spermatic animals contained the great animal in miniature, he says, "Progeneratio animalis ex animalculo in seminibusmasculinis omni exceptione major est; nam etiamsi in animalculo ex semine masculo unde ortum est, figuram animalis conspicere nequeamus, attamen satis superque certi esse possumus figuram animalis ex qua animal ortum est, in animalculo quod in semine masculo reperitur, conclusam jacere sive esse; & quanquam mihi sæpius conspectis animalculis in semine masculo animalis, imaginatus fuerim me posse dicere, en ibi caput, en ibi humeros, en ibi femora; attamen eum ne minima quidem certitudine de iis judicium ferre potuerim, hujusque certi quid statuere supersedeo, donec tale animal, cujus semina mascula tam magna erunt, ut in iis figuram creaturæ ex qua provenit, agnoscere queam, invenire secunda nobis concedat fortuna." This fortunate chance, which Leeuwenhoek desires, presented itself to Mr. Needham. Every part of the spermatic animals of the calmar are easy to be seen without a microscope; but they are not young calmars, as Leeuwenhoek thinks, nor even animated, although they are in motion, but only machines which must be regarded as the first produce of the union of organic particles.

Although Leeuwenhoek had not such an opportunity of undeceiving himself, he nevertheless had another phenomena which ought to have had that effect; for example, he had remarked that the spermatic animals of a dog often change their figures, especially when the liquor was on the point of evaporating; that these pretended animals had a hole in the head when they were dead, and that this hole did not appear when they were alive; he had seen that the part which he looked upon as the head was full and plump when it was alive, and flaccid and flat when dead. All this ought to have led him to doubt whether these moving bodies were real animals; and consider it as agreeing better with a machine, which empties itself like that of the calmar, than with a moving animal.

I have said that these moving bodies, these organic particles, do not move like animals, nor have an interval of rest. Leeuwenhoek has observed the same: "Quotiescunque, says he, animalcula in semine masculo animalium fucrim contemplatus, attamen illa se unquam ad quietem contulisse, me nunquam vidisse, mihi dicendum est, si modo sat fluidæ superesset materiæin qua sese commode movere poterant; et eadem in continuo manent motu, & tempore quo ipsis moriendum appropinquante, motus magis magisque deficit, usquedum nullus prorsus motus in illis agnoscendus sit." It appears difficult to conceive that animals can exist, from the moment of their birth till that of their death, in a continual rapid motion without the least interval of rest; and I cannot possibly imagine how these animals in the semen of a dog, which Leeuwenhoek saw the seventh day in as rapid motion as they were when they were first taken from the body of the animal, preserved a motion during that time so exceedingly swift, that no animal has sufficient power to move in for an hour; especially if we consider the resistance which proceeds from the density and the tenacity of the liquor. This kind of continued motion, on the contrary, agrees with the organic particles, which, like artificial machines, produce their effects in a continual operation, and which stop when that effect is over.

Among the great number of Leeuwenhoek's experiments, he, without doubt, often perceived spermatic animals without tails; and he endeavours to explain this phenomenaby a supposition; for example, he says, speaking of the semen of a cod, "Ubi vero ad lactum accederem observationem, in iis partibus quas animalcula esse censebam neque vitam neque caudam dignoscere potui; cujus rei rationem esse existimabam, quod quamdiu animalcula natando loca sua perfecte mutare non possunt tam diu etiam cauda concinne circa corpus maneat ordinata, quodque ideo singula animalcula rotundum repræsentent corpusculorum."

It would have been better to have said, as it in fact is, that the spermatic animals of these fish have tails at certain times and none at others, than to suppose their tails twisted so exactly round their bodies as to give them the shape of a globule. But this must not lead us to think that Leeuwenhoek only attended to the moving bodies which he saw with tails, but rather that he did not describe the others, because, although they were in motion, he did not regard them as animals; and this is the cause that all the spermatic animals he has depicted resemble each other, and drawn with tails, since he only took them for real animals in that state; and that when he saw them under other forms, he thought them imperfect,or rather that they were dead. On the whole it appears, by my experiments, that far from displaying their tails the more as they are in a more perfect condition of swimming, as Leeuwenhoek says, they, on the contrary, lose their tails in a gradual manner, till at last these tails, which are no more than foreign bodies of the animalcules, and which they drag after them, entirely disappear.

In another part Leeuwenhoek, speaking of the spermatic animals of man, says, "Aliquando etiam animadverti inter animalcula particulas quasdam minores & subrotundas; cum vero se ea aliquoties eo modo oculis meis exhibuerint, ut mihi imaginarer eas exiguis instructas esse caudis, cogitare cœpi annon hæ forte particulæ forent animalcula recens nata; certum enim mihi est ea etiam animalcula per generationem provenire, vel ex mole minuscula ad adultam procedere quantitatem: & quis sit annoa ea animalcula, ubi moriuntur, aliorum animalculorum nutritioni atque augmini inserviant?" By this passage it appears that Leeuwenhoek had seen animals without tails in the seminal liquor of a man, and that he is obliged to suppose them to be just born, and not adult; but I have observed quite the contrary; for themoving bodies are never larger than when they separate from the filaments, and begin to move. When they are entirely disengaged from the mucilage they become smaller, and continue decreasing as long as they remain in motion. With respect to the generation of these animals, which Leeuwenhoek speaks of as certain, I am persuaded no sign of generation has ever been discovered; all he says is advanced on mere suppositions, which it is easy to prove by his own observations; for example, he says that the milt of certain fish, as the cod, fills by degrees with seminal liquor, which after the fish has emitted, the milt dries up, leaving only a membrane destitute of any liquor. "Eo tempore, says he, quo ascellus major lactes suos emisit, rugæ illæ, seu tortiles lactium partes, usque adeo contrahuntur, ut nihil præter pelliculas seu membranæ esse videantur." How then does he understand that this dry membrane, in which there is no longer either seminal liquor or animalcules, can reproduce animals of the same kind the succeeding year? if there was a regular generation in these animals, there could not be this interruption, which in most fishes lasts for a whole year. To draw himself out of this difficulty, he says, "Necessario statuendum erit, ut ascellus majorsemen suum emiserit, in lactibus etiamnum multum materiæ seminalis gignendis animalculis aptæ remansisse, ex qua materia plura oportet provenire animalcula seminalia quam anno proxime elapso emissa fuerant." This supposition, that there remains something in the seminal liquor in the milts to produce spermatic animals for the succeeding year, is absolutely contrary to observations, for the milt is in this interval only a thin and absolutely dry membrane. But what reply can be made to a still further opposition to this point, there being fish like the calmar, the seminal liquor of which is not only renewed every year, but even the reservoir which contains it? Can it be said, that there remains a seminal matter in the milt for the production of the animals for the succeeding year, when even the milt does not remain? it is therefore very certain that these pretended spermatic animals are not multiplied, like other animals, by the mode of generation; which alone is sufficient to make us presume, that those particles which move in the seminal liquors are not real animals. Thus Leeuwenhoek, who in the passage above quoted says, it is certain that spermatic animals multiply and propagate by generation, nevertheless owns, in anotherpart, that the manner in which these animals are produced is very obscure, and that he leaves to others the task of clearing up this matter. "Persuadebam mihi," says he, speaking of the spermatic animals of the dormouse, "hæcce animalcula ovibus prognasci, quia diversa in orbem jacentia & in semet convoluta videbam; sed unde, quæso, primam illorum originem derivabimus? in animo nostro concipiemus horum animalculorum semen jam procreatum esse in ipsa generatione, hocque semen tam diu in testiculis hominum hærere, usquedum ad annum ætatis decimum-quartum vel decimum-quintum aut sextum pervenerint, eademque animalcula tum demum vita donari vel in justam staturam excrevisse, illoque temporis articulo generandi maturitatem adesse! sed hæc lampada aliis trado." I do not think it necessary to make any remarks on what Leeuwenhoek says on this subject: he saw spermatic animals without tails, and round, in the seed of a dormouse; "in semet convoluta," says he, because he supposes that they should have tails, and instead of being certain, as he before had been, that the animals propagate by generation, he here seems convinced of the contrary. But when he had observed the generation of pucerons,and was assured[X]that they engendered without copulation, he caught the idea to explain the generation of spermatic animals. "Quemadmodum, says he, animalcula hæc quæ pediculorum antea nomine designavimus (the pucerons) dum adhuc in utero materno latent, jam prædita sunt materia seminali ex qua ejusdem generis proditura sunt animalcula, pari ratione cogitare licet animalculæ in seminibus masculinis ex animalium testiculis non migrate seu ejici quin post se relinquant minuta animalcula aut saltem materiam seminalem ex qua iterum alia ejusdem generis animalcula proventura sunt idque absque coitu; eadem ratione qua supradicta animalcula generari observavimus." This supposition gives no more satisfaction than the preceding: for we do not understand by this comparison of the generation of these animalcules with that of a puceron, why they are not found in the seminal liquor of a man, before he has attained the age of fourteen or fifteen years; nor do we know from whence they proceed, nor how they are renewed every year in fish, &c. and it appears, that whatever efforts Leeuwenhoek made to establish the generation of spermatic animals on some probability, it still remainedan entire obscurity, and would, perhaps, perpetually have remained so, if the preceding experiments had not evinced that they are not animals, but moving organic particles contained in the nutriment the animal receives, and which are found in great numbers in the seminal liquor, which is the most pure, and in the most organic extracts drawn from this nutriment.

[X]See vol. II. page 499, and vol. III. page 271.

Leeuwenhoek acknowledges that he had not always found animalcules in the seminal liquor of males; in that of the cock, for example, which he had often examined, he saw spermatic animals in the form of eels but once, and some years after he could not discover any under that form, but observed some with large heads and tails, which his designer could not perceive. He says also, that one season he could not find living animals in the seminal liquor of the cod. All these disappointments proceeded from his desire of finding tails to these animals; and although he perceived little bodies in motion, he did not consider them as animals, because they were without tails, notwithstanding it is under that form they are generally seen, either in seminal liquors, or infusions of animal or vegetable substances. He says, inthe same place, that he was never able to make his designer perceive the spermatic animalcules of a cod, which he had so often seen himself.—"Non solum, says he, ob eximiam eorum exilitatem, sed etiam quod eorum corpora adeo essent fragilia, ut corpuscula passim dirumperentur; unde factum fuit ut nonnisi rare, nec sine attentissima observatione, animadverterem particulas planas atque ovorum in morem longas, in quibus ex parte caudas dignoscere licebat; particulas has oviformes existimavi animalcula esse dirupta, quod particulæ hæ diruptæ quadruplo fere viderentur majores corporibus animalculorum vivorum." When an animal of any kind ceases to live, it does not then suddenly alter its form, and from being long, like a thread, becomes round like a ball; neither does it become four times larger after its death than it was before. Nothing that Leeuwenhoek says here agrees with the nature of animals; but, on the contrary, the whole corresponds with a kind of machine, which, like those of a calmar, empty themselves after having performed their functions. But let us pursue this observation; he says, he has seen the spermatic animals of the cod in different forms, "multa apparebant animalcula sphærampellucidam representantia;" he has also seen them of different sizes, "hæc animalcula minori videbantur mole, quam ubi eadem antehac in tubo vitreo rotundo examinaveram."

There needs nothing more to shew that there are no constant and uniform species of these animalcules; and that consequently they are not animals, but only organic particles in motion, which, by their different combinations, take different forms and sizes. These organic moving particles are found in great quantities in the extract and residue of our nutriment. The matter which adheres to the teeth, and which in healthy people has the same smell as the seminal liquor, is only a residue of the food, and a great number of these pretended animals are also found there, some of which have tails, and resemble those in the seminal liquor. Mr. Baker had four different kinds of them engraved, and which were all of a cylindrical or oval make, or globules with and without tails. I am persuaded, after having strictly examined them, that not any of them are real animals, but are like those in the seed, only living organical parts of the nutriment which present themselves under different forms, Leeuwenhoek,who did not know how to account for these pretended animals in the matter which adhered to the teeth, supposed them to proceed from certain food they were previously in, as cheese, &c. but we find them among the teeth of those who do not eat cheese, as well as in those that do; besides, they have not the least resemblance to mites, nor the other animalcules seen in rotten cheese. In another place he says, these animals of the teeth may proceed from the cistern water that is drank, because he observed animals like them in dew and rain water, especially in that which stagnates upon lead and tiles; but with which we can prove there is not the least resemblance.

Most seminal liquors dilute of themselves, and liquefy when exposed to the air or a certain degree of cold; but they thicken when a moderate degree of heat is communicated to them. I have exposed some of these liquors to a very intense cold, as water on the point of freezing, but it did no injury to these supposed animals; they continued to move with the same swiftness, and as long as those which had not been so exposed, but those which had suffered but a little warmth soon ceased to move, because the liquor thickened. If the movingbodies were animals, they were of a complexion and temperament quite different from all others, to whom a gentle and moderate heat strengthens their powers and motions, which the cold stops and destroys.

Notwithstanding it may be thought I have dwelt too long upon this subject, I cannot conclude it without making one remark, from which some useful conclusions may be drawn. These pretended spermatic animals, which are only living organic particles of the nutriment, not only exist in the seminal liquors of the two sexes, and in the residue of the nutriment which adheres to the teeth, but also in the chyle and excrements. Leeuwenhoek having met with them in the excrements of frogs, and other animals, which he dissected, was at first very much surprised, and notable to conceive from whence these animals proceeded, so entirely like those he had observed in the seminal liquors, accuses himself of having, in dissecting the animal, opened the seminal vessels, and that the seed had by that means been mixed with the excrements. But having afterwards found them in the excrements of other animals, and even in his own, he no longer knew to what to attribute them. Leeuwenhoek,it is worthy remark, never met with them in his own excrements, but when they were liquid. Every time he was disordered and the stomach did not perform its functions, and was relaxed, he discovered these animalcules; but when the concoction of the food was well performed, and the excrement was hard, there was not a single one, although it was diluted with water. This seems perfectly to agree with all we have before advanced: for when the stomach and intestines perform their functions, the excrements are only the grosser parts of the nutriment; and all that is really nutritive and organic passes into the vessels which serve to nourish the animal; whereas if the stomach and intestines are not in a condition to comminute the food, then it passes with the inanimate parts, and we find the living organic molecules in the excrements; from whence it may be concluded, that those which are often lax must have less seminal liquor, and be less proper for generation, than those of a different habit of body.

In all I have said, I constantly supposed the female furnished a seminal liquor, which was as necessary to generation as that of the male. I have endeavoured to establish inChap. I.thatevery organized body must contain living organic particles, and I have endeavoured to prove Chap.II.andIII.that nutrition and reproduction operates by the same cause; that nutrition is made by the intimate penetration of these organic particles through each part of the body, and that reproduction operates by the superfluity of these same organic particles collected together from all parts of the body and deposited in proper reservoirs. I have explained in Chap.IV. how this theory must be understood in the generation of man and animals which have sexes. Females then being organized bodies like males, they must also have some reservoirs for the superfluity of organic particles returned from every part of their bodies. This superfluity cannot come there through any other form than that of a liquor, since it is an extract of all parts of the body; and this liquor is that to which I have given the name of the female semen.

This liquor is not, as Aristotle pretends, an infecund matter of itself, which enters neither as matter nor form into the business of generation, but as essentially prolific as that of the male, containing characteristic parts of the feminine sex, which the female alone can produce, the same as the male contains particles necessaryto form the masculine organs; and each of them contains every other organic particle that can be looked on as common to both sexes; which causes that, by their mixture, the daughter may resemble her father, and the son his mother. This semen Hippocrates says, is composed of two liquors; the one strong, for the production of males; and the other weak, for the production of females. But this supposition is too extended; I do not see how it is to be conceived that a liquor, which is the extract of every part of the female body, should contain particles for the formation of the male organs.

This liquor must enter by some way into the matrix of animals which bear and nourish their fœtus within the body, and in others, as oviparous animals, it must be absorbed by the eggs, which may be looked upon as portable matrixes. Each of these matrixes contains a small drop of this prolific liquor of the female, in the part that is called thecicatrice. When there has been no communication with the male, this prolific drop collects under the form of a small mole, or mass, as Malpighius observes; but when impregnated by that of the male; it produces a fœtus which receives its nutriment from the juices of the egg.

Eggs, instead of being parts generally found in every female, are therefore only instruments made use of by Nature to serve as the matrix in females which are deprived of that organ. Instead also of being active and essential to the first fecundation, they only serve as passive and accidental parts for the nutrition of the fœtus already formed by the mixture of the liquor of the two sexes in a particular part of this matrix. Instead also of being existing bodies, inclosed,ad infinitum, one within the other, eggs, on the contrary, are bodies formed from the superfluity of a more gross and less organic part of the food, than that which produces the seminal and prolific liquor; and are in oviparous females something equivalent, not only to the matrix, but even to the menstrua in the viviparous.

We should be perfectly convinced, that eggs are only destined by Nature to serve as a matrix in animals who have not that viscera, by those females producing eggs independant of the male. In the same manner as the matrix exists in viviparous animals, as a part appertaining to the female sex, hens, which have no matrix, have eggs in their room, which are successively produced of themselves, and necessarily exist in the female independently ofany communication with the male. To pretend that the fœtus is pre-existing in the eggs, and that these eggs are contained,ad infinitum, within each other, is nearly the same as to pretend that the fœtus, is pre-existing in the matrix, and that the matrix of the first female inclosed all that ever were or will be produced.

Anatomists have taken the wordeggin several acceptations and meanings. When Harvey took for his motto,Omnia ex ovo, he understood by the word egg, as applied to viviparous animals, the membrane which includes the fœtus and all its appendages: he thought, he perceived this egg, or membrane, form immediately after the copulation of the male and the female. But this egg does not proceed from the ovium of the female; and he has even maintained, that he did not remark the least alteration in this testicle, &c. We perceive there is here nothing like what is commonly understood by the word egg unless the figure of the bag may be supposed to have some resemblance thereto. Harvey, who dissected so many viviparous females, did not, he says, ever perceive any alteration in the ovaria; he looked on them even as small glands, perfectly useless to general ion,[Y]althoughthey undergo very remarkable changes and alterations in them, since we may perceive in cows the glandular bodies grow from the size of a millet seed to that of a cherry. This great anatomist was led into this error by the smallness of the glandular bodies in the species of deer, to which he principally paid his attention. C. Peyerus, who also made many experiments on them, says, "Exigui quidem sunt damarum testiculi, sed post coitum fœcundum, in alterutro eorum, papilla, sive tuberculum fibrosum, semper succrescit; scrofis autem prægnantibus tanta accidit testiculorum mutatio, ut mediocrem quoque attentionem fugere nequeat."[Z]This author imagines, with some reason, that the minuteness of the testicles of does, is the cause of Harvey's not having remarked the alterations; but he is wrong in advancing that the alterations he had remarked, and which had escaped Harvey's notice, did not happen till after impregnation.

[Y]See Harvey Exercit. 64 and 65.

[Z]Vide Conradi Peyeri Merycologia.

It appears that Harvey was deceived in many other essential points; he asserts, that the seed of the male does not enter into the matrix of the female, and even that it cannot; yet Verheyen found a great quantity of the male seed in thematrix of a cow, which he dissected six hours after copulation.[AA]The celebrated Ruysch asserts, that having dissected a woman who had been caught in the act of adultery, and was assassinated, he found, not only in the cavity of the matrix, but also in the trunks, a quantity of the seminal liquor of the male,[AB]Valisnieri affirms, that Fallopius and other anatomists had also discovered male seed in the matrix of many women. After the positive testimony of these great anatomists, there can remain no doubt but Harvey was deceived in this important point; especially when to these are added that of Leeuwenhoek, who found the male seed in the matrix of a great number of females of different species.

[AA]See Verheyen Sup. Anat. Tra. v. cap. iii.

[AB]See Ruysch, Thes. Anat. p. 90, tab.VI, fig. I.

Harvey makes another error in speaking of an abortion in the second month, where the mass was as large as a pigeon's egg, but without any fœtus regularly formed; whereas, it is maintained by Ruysch, and many other anatomists, that the fœtus is perceptible, even to the naked eye, in the first month. The History of the Academy mentions a fœtus, that was completely formed in twenty-one days after impregnation. If to these authorities we add that ofMalpighius, who perceived the chicken in the cicatrice, immediately after the egg was laid by the hen, we cannot doubt, but that the fœtus is formed immediately after copulation; consequently, we must not pay any credit to what Harvey says on the parts increasing one after the other by juxta-position, since they are all existent from the first, and gradually expand until the whole is complete.

De Graaf took the acceptation of the word egg in a quite different light to Harvey: he insists that the testicles of women were true ovaries, and contain eggs like those of oviparous, animals, only that they are much smaller, do not quit the body, and are never detached till after impregnation, when they descend from the ovary into the horns of the matrix. The experiments of De Graaf have contributed most to establish the existence of these pretended eggs, which yet is not at all founded; for this famous anatomist is deceived, first, by mistaking the vesicles of the ovarium for eggs, whereas they are inseparable from it, form parts of its substance, and are filled with a kind of lymph. Secondly, he is also deceived when he considers the glandular bodies to be the covering of those eggs, or vesicles; for it is certain, by Malpighius's,Valisnieri's, and my own observations, that the glandular bodies neither surround nor contain one of those vesicles. Thirdly, he is deceived still more when he supposes the glandular body is never formed till after fecundation; as they are invariably found in every female who has attained the age of puberty. Fourthly, he is no less deceived when he believes that the globules which he saw in the matrix, and which contained the fœtuses, ware the same vesicles, or eggs, which had fallen from the ovariam, and which, he remarks, were become ten times smaller than they were in the ovary. This remark alone, one would imagine, Should have made him perceive his error. Fifthly, he is wrong in saying that the glandular bodies are only the coverings of the fecundated eggs, and that the number of coverings, or empty follicles, always answer to the number of fœtuses. This assertion is entirely contrary to truth: for on the testicles of all females we find a greater number of glandular bodies, or cicatrices, than there are productions of fœtuses, and they are also found in those which have never brought forth. To this we may add, that neither he, Verheyen, nor any other person, have ever seen these eggs, much less thesepretended coverings, on which they have, notwithstanding, established their system.

Malpighius, who perceived the growth of the glandular bodies in the female testicles, was deceived when he thought he had seen the egg in their cavities, since they contain only liquor; nor indeed has anything like an egg ever been discovered.

Valisnieri, who was not deceived in facts, has yet drawn false conclusions in asserting that, although neither himself, nor any anatomist in whom he could confide, ever found the egg in the cavity of the glandular body, yet it must there exist.

Let us, therefore, examine what may be fairly called the real discoveries of these naturalists. Graaf was the first who perceived there were alterations in the female testicles; and he had reason to affirm, they were parts essential and necessary to generation. Malpighius demonstrated that these alterations were occasioned by the glandular bodies which grew to perfect maturity, afterwards they become flaccid, obliterated, and left only a slight cicatrice remaining. Valisnieri has placed this discovery in a very clear light; he has shewn that these glandular bodies are found in the testicles of every female; that theyare augmented considerably in the season of love, that they increase at the expence of the lymphatic vesicles of the testicles, and that at the time of their maturity they were hollow and filled with liquor. This, then, is all that can be reduced to truth on the subject of the pretended ovaries and eggs of viviparous animals. What must we conclude therefrom? Two things appear very evident: the one, that there does not exist any eggs in the female testicles; the other, that there exists a liquor in the vesicles of the testicle, and in the cavity of the glandular bodies. We have demonstrated by the preceding experiments, that this last liquor is the true seed of the female, since it contains, like that of the male, spermatic animals, or rather organic moving particles.

We must, therefore, now be assured, that females have, as well as males, a seminal liquor. After all that has been advanced, we cannot doubt but the seminal liquor is the superfluity of the organic nutriment, which is sent back from all parts of the body into the testicles and seminal vesicles of the males, and into the testicles and glandular bodies of females. This liquor, which issues by the nipple of the glandular bodies, continually sprinklesthe horns of the matrix, and may easily procure admission either by the suction of the membrane of these horns, or by the little opening which is at the upper extremity, and thus enter into the matrix; but in the supposition of these pretended eggs, which were ten or twenty times larger than the opening of the horns of the matrix, we cannot comprehend how they could enter therein.

The liquor emitted by females, when they are excited, and which, according to de Graaf, issues from the neck of the matrix, and the orifice of the urethra, may be a superabundant portion of the seminal liquor which continually distills from the glandular bodies on the trunks of the matrix. But, possibly, this liquor may be a secretion of another kind, and perfectly useless in generation. To decide this question observations with a microscope are requisite; butallexperiments are not permitted even to philosophers. I can only say, that I am inclined to believe that the same spermatic animals would be met with in this liquor as in that of the glandular bodies. I can quote an Italian doctor on this subject, who made this observation with attention, and which is thus related by Valisnieri: "Aggiugne il lodato fig. Bonod'avergli anco veduti (animali spermatici) in questa linfa o siero, diro cosi voluttuoso, che nel tempore dell'amorosa zuffa scappa dalle femine libidinose, senza che si potesse sospettare che fossero di que' del maschio, &c." If this circumstance is true, as I do not doubt, it is certain, that this liquor is the same as that found in the glandular bodies, and that, consequently, it is the true seminal liquor: and although anatomists have not discovered the communication between the vacuities of de Graaf and the testicles, that does not prevent it being once in the matrix, from issuing out by the vacuities about the exterior orifice of the urethra.

From hence we must conclude that the most abandoned women will be the least fruitful, because they emit that liquor which ought to remain in the matrix for the formation of the fœtus. Thus we see why common prostitutes seldom have children, and why women in hot countries, where they have stronger desires than in the cold, are much less fertile; but we shall have occasion to speak of this hereafter.

It is natural to think that the seminal liquor of the male or female would not be fertile but when it contains moving bodies; neverthelessthat is still a question, and I should be led to think, as there are different states of this liquor, that in which these organic particles are seen in motion is not absolutely necessary for the purpose of generation. The Italian physician, above quoted, never perceived spermatic animals in his semen till he had attained a middle age, although he was father of several children before, and continued to have them afterwards.

These spermatic bodies, which move, may be looked upon as the first assemblages of the organic molecules which proceed from every part of the body; when a quantity of them collect they may be perceived with the microscope; but if they collect only in small quantity the body which they form will be too minute to be perceived, and in this case we shall not be able to distinguish any in the seminal liquor. A very long continuance of observations would be necessary to determine what can be the cause of all the differences remarked in the states of this liquor.

I can assert, from having often tried it, that by infusing the seminal liquors in water closely corked, at the end of three or four days an infinite multitude of moving bodies will be found, although the seminal liquors had no motion onbeing first taken from the body of the animal. Flesh, blood, chyle, urine, nay all animal or vegetable substances, contain organic particles, which move at the end of some days in an infusion of water; they appear to act and move nearly in the same manner, and though produced from different bodies are perfectly similar, without any of them having a power peculiar to themselves. If these bodies must absolutely be termed animals, it must be allowed they are so imperfect that they ought to be looked upon as the outlines of them, or rather as bodies simply composed of particles the most essential to the existence of an animal; for natural machines, such as those found in the roe of a calmar, although they put themselves in action at certain times, are certainly not animals, although they are organized, acting, and, as I may say, living beings.

If it is once allowed, that the productions of Nature follow in an uniform order, and advance by imperceptible degrees and links, we shall have no difficulty in conceiving there are organic bodies existing, which belong neither to animals, vegetables, nor minerals.

It is certain, however, that all animals and vegetables contain an infinity of organic livingmolecules. These molecules successively take different forms, and different degrees of motion and activity, according to different circumstances They are in a much greater number in the seminal liquor of both sexes, and in the germs of plants, than in other parts of the animal or vegetable. There exists, then, a living substance in animals and vegetables, common to both, and which substance is necessary to their nutrition. An animal procures nutriment from an animal or vegetable substance, and the vegetable can likewise be nourished from an animal or vegetable in a decomposed state. This nutritive substance, common to both, is always living, always active, and produces an animal or vegetable, as it finds an internal mould or an analogous matrix, as we have explained in the first chapters; but when this active substance collects in great abundance, in those parts where it can unite, it forms in the animal body other living creatures, such as the tape-worm, ascarides, and worms, which are sometimes found in the veins, in the sinus of the brain, in the liver, &c. These kinds of animals do not owe their existence to the animals of the same species, and we may, therefore, suppose, they are produced by this organicmatter when it is extravasated, or is too abundant for the lacteal vessels to absorb. We shall hereafter have occasion to examine more largely the nature of those worms, and many other animals which are formed in a similar manner.

When this organic matter, which may be looked on as an universal seed, is collected in any great quantity, as in the seminal liquors, and in the mucilaginous parts of the infusion of plants, its first effect is to vegetate, or rather to produce vegetating beings. These zoophytes swell, extend, ramify, and produce globules, ovals, and other small bodies, of different figures, which have all a kind of animal life, a progressive motion, which is often very swift, and sometimes very slow. These globules themselves decompose, change their figures, and become smaller; and in proportion as they diminish in size the rapidity of their motion augments.

I have sometimes thought that the venom of the viper, and other active poisons, even that of the bite of a mad dog, might possibly be this active matter too rarefied; but I have not as yet had time to make the experiments which I had projected on this matter, as well as ondrugs used in medicine; all that I can at present ascertain is, that all infusions of the most active drugs swarm with moving bodies, which form therein in much less time than in other substances.

Almost all microscopic animals are of the same nature as the organized bodies which move in the seminal liquor, in the infusions of vegetables and the flesh of animals; the eel-like bodies in flour, vinegar, and water, in which lead has been soaked, are beings of the same nature as the first, and have a like origin.

CHAPTER IX.

VARIETIES IN THE GENERATION OF ANIMALS.

The matter which serves for the nutrition and reproduction of animals and vegetables is therefore the same; it is a productive and universal substance, composed of organic molecules, and whose union produces organized bodies. Nature always works on thesame fund, which is inexhaustible, but the means she employs to stamp its value are different, and these differences, or general agreements, deserve attention, because it is from thence we must derive our reasons to account for exceptions and particular varieties.

In general large animals are less productive than small. The whale, elephant, rhinoceros, camel, horse, the human species, &c. only produce one, and very seldom two, at a birth; whereas small animals, as rats, herrings, insects, &c. produce a great number at a time. Does not this difference proceed from there being more food required to support a large body than to nourish a small one, and from hence the former has less superfluous organic particles, which would convert into semen, than the latter? It is certain that small animals eat more in proportion than large ones; but it is likewise probable that the prodigious multiplication of the small animals, as bees, flies, and other insects, may be attributed to their being endowed with very fine and slender limbs and organs, by which they are in a condition to chuse what is most substantial and organic in the vegetable or animal matters from whence they derive their nutriment. Abee, who lives on the purest parts of flowers, certainly receives more organic particles in proportion than a horse who feeds on the grosser parts of vegetables, hay, &c. The horse produces but one at one time, whereas the bee will bring forth three thousand.

Oviparous animals are in general smaller than the viviparous, and produce also more at a birth. The duration of the fœtus in the matrix of viviparous animals likewise opposes their increase, nor can there be any new generation take place during gestation, or while they are suckling their young; whereas oviparous animals produce at the same time both matrix and fœtuses, which they cast out of the body, and are therefore almost always in a state of reproduction; and it is well known that by preventing a hen from setting, and largely feeding, the number of her eggs will be considerably increased. If hens cease to lay when they sit, it is because they have ceased to feed; and it is the fear lest their eggs should not produce which causes them not to quit their nests but once a day, and that for a very short time, during which they take a little nutriment, but not one-tenth part of what they take at other times.

Animals which produce but a small number at a time, acquire the chief part of their growth before they are fit for engendering, whereas those which multiply numerously generate before they have received half their growth. The human species, the horse, the ass, the goat, and the ram, are not able to engender until they have obtained nearly the whole of their growth. It is the same with pigeons and other birds, who lay but a few eggs; but those which produce in great numbers, as poultry, fish, &c. engender much sooner. A cock is capable of engendering at the age of three months, when he has not attained a third part of his growth; a fish, which at the end of twenty years will weigh thirty pounds, engenders in the first or second year, when perhaps it does not weigh half a pound. But exact observations on the growth and duration of the life of fish are still wanting: their age may be nearly known by examining the annual layers of their scales; but we are not certain how far that may extend. I have seen carp in the Comte de Maurepas' canals, at his castle at Pont Chartrain, which were said to be 150 years old, and they appeared as brisk and lively as the common carp. I will notsay, with Leeuwenhoek, that fish are immortal, or at least can never die with age; all must perish in time, that is; all which have a beginning, a birth, must arrive to an end, or death; but fish, living in an uniform element, and being sheltered from the vicissitudes and all the injuries of the air, must live a longer time in the same state than other animals, especially if these vicissitudes of the air be, as a great philosopher asserts, the principal causes of the destruction of living beings. But what must contribute to the long duration of their life is, that their bones are softer than those of other animals, and do not harden with age. The bones of fish lengthen, and grow thick without taking any more solidity; whereas the bones of other animals continually increase in hardness and density, until at length, being absolutely full, the motion of their fluid ceases, and death ensues. In their bones the repletion or obstruction, which is the cause of natural death, is formed by such slow and insensible degrees, that fish must require much time to arrive at what we call old age.

All quadrupeds covered with hair are viviparous; all those covered with scales oviparous. May we not then believe than in oviparousquadrupeds, a much less waste is made by transpiration, than the cloathing of scales retains; whereas in animals covered with hair this transpiration is more free and abundant? and is it not partly by this superabundance of nutriment, which cannot be carried off by transpiration, that those animals multiply so abundantly, and are enabled to go so long without food? All birds and all insects that fly are oviparous, excepting some kinds of flies which bring forth their young alive. These flies have no wings at their birth, but they shoot out and grow by degrees, and which they cannot use before they are of full growth. Scaly fish are likewise oviparous; as are all reptiles which have no legs, such as snakes and different kinds of serpents; they change their skins, which are composed of small scales. The viper is only a slight exception to the general rule, for it is not truly viviparous, as it produces eggs, from which the young are hatched; it is certain this is performed in the body of the mother, who instead of casting those eggs, like other oviparous animals, she retains and hatches them in her own body. The salamander, in which eggs and young ones are found at the same time, as observed by M. deMaupertuis, is an exception of the same kind in oviparous quadrupeds.

Most animals are perpetuated by copulation; yet many birds seem only strongly to compress the females; indeed the ostrich, Crane, and some few others, are so well supplied as to leave intromission no ways equivocal. Male fish approach the female in the spawning time; they seem even to rub their bellies against each other, for the male often turns upon its back to meet the belly of the female; but the necessary part for copulation does not exist in them; and the male fish approaches the female only to emit the liquor in their milts on the eggs, which the female then deposits; and it seems rather to be attracted by the eggs than the female; for when she ceases throwing out the eggs, he instantly forsakes her, and with eagerness pursues the eggs, which the stream carries away, or that the wind disperses. Male fish may be seen to pass and repass every spot where eggs are deposited several times. It is certainly not for the love he bears the female that all these motions are made, because it is not to be presumed he always knows her; often being seen to emit his liquor on all eggs that he comes near,and that often before he has met with the female to which they belonged.

There are therefore animals, distinguished by sexes, which have proper parts for copulation, and some which are deficient in them; others, as snails, have both, and the two sexes in the same individual; others, as vine-fretters, have no sex, and engender in themselves separately; although they couple together when they please, we cannot determine whether that is a conjunction of sexes; if it is so, we must suppose that Nature has included in this small individual more faculties for generation than in any other kind of animal, and that it not only has the power of reproducing distinctly, but also the means of multiplying by the communication of another individual.

But whatever difference takes place in generation, Nature, by a new production, prepares the body for it, and which, whether manifested outwardly, or concealed internally, always precedes generation. The ovaries of oviparous animals, and the testicles of female viviparous animals, before the season of impregnation, experience a considerable change. Oviparous animals produce eggs, which at first are attached to the ovaries, by degreesthey increase in size, until they fall into the canal of the matrix, where they acquire their white membranes, and shell. This production has marks of the fecundity of the female, and without which generation cannot be performed: so in viviparous females there are always one or more glandular bodies on the testicles, which by degrees grow under the membrane that surrounds them; these glandular bodies enlarge and pierce, or rather impel and lift up the membrane of the testicle; when their maturity is complete, a small slit or several small holes appear at their extremities, by which the seminal liquor escapes, and falls into the matrix: these glandular bodies are new productions that precede generation, and without which there would not be any.

In males there is also a similar change which always precedes their capacity for generating. In oviparous animals a great quantity of liquor fills a considerable reservoir, and which reservoir itself is sometimes formed every year; as in the calmar and some other fish. The testicles of birds swell surprisingly just preceding their amorous season. In viviparous males the testicles also swell considerably in those who haveseasons, and in general there is a swelling and an extension of the genital members in all species, which, although it be external, must be regarded as a new production necessarily preceding generation.

In the body of every animal, male or female, new productions are formed which precede generation; and when there is no real production there is always a swelling, and considerable extension in some of the parts. There are species in which this new production is not only manifest, but even the whole body seems to be renewed before generation can be performed; as is the case with insects whose various metamorphoses seem to be only for the purpose of generating; for the growth of the animal is completed before it is transformed. It ceases from taking nutriment, has no organs for generation, no means of converting the nutritive particles, of which they abound, into eggs or seminal liquor, and therefore this superfluity unites and moulds itself at first into a form something like that of the original. The caterpillar becomes a butterfly, because, for these reasons, it is unable to produce small organized beings like itself; the organic particles, always active, take another form, by uniting,whose figure answers in part, and even in essential constitution, to that of the caterpillar, but in which the organs of generation are developed, and may receive and transmit the organic particles of the nutriment which forms the eggs, and the individuals of the species. The individuals which proceed from the butterfly ought not to be butterflies, because the nutriment, from whence the organic particles proceed, was taken while in the form of caterpillars; the produce therefore must be similar, and not butterflies, which is only an occasional production of the superabundant nutriment; a method adapted by Nature to accomplish the purposes of generation in these species, as by the glandular bodies and milts in other animals.

When the superabundant quantity of organic nutriment is not great, as in man and most large animals, generation is not made till the growth of the animal is nearly complete, and then it is confined to the production of a small number of individuals. When these particles are more abundant, as in many kinds of birds, and in oviparous fishes, generation is completed before the animal has received its full growth, and their production of individualsis very numerous. When the quantity of particles is still greater, as in insects, it first forms a large organic body, which, though retaining the essential constitution of its original, differs in many parts, as the butterfly from the caterpillar, but shortly produces an astonishing number of young, similar in form to the animal which selected the nutriment. When the superabundance is greater still, and when at the same time the animal has the necessary organs for generation, as the vine-fretter, it immediately produces a generation in every individual, and afterwards a transformation, like other insects. The vine-fretter becomes a fly, but cannot produce any thing, because it is only the remainder of the organized particles which had not been made use of in the production of the young.

Almost every animal except man has stated times for generation. Spring is marked out for birds. Carp, and many kinds of fish, spawn in June and August. Barbel, and other kinds, in spring. Cats have three seasons, in January, May, and September. Roebucks, in December. Wolves and Foxes, in January. Horses, in summer. Stags, in September and October; and almost all insects generate inautumn: these last seem to be totally exhausted by generation, and die a short time after. Other animals, though not exhausted, become extremely lean and very weak, and require a considerable time to repair the loss which is made of the organic substance. Others are exhausted still less, and are soon restored to an engendering state; while man is scarcely in the least affected; his loss is speedily repaired, and therefore may be said to be at all times in a state for propagation; all which depends solely on the particular construction of the animal organs. The grand limits Nature has placed in the mode of existence are equally conspicuous in the manner of receiving and digesting the food, in the manner of retaining it in, or excluding it from, the body, and in the means by which the organic molecules, necessary for reproduction, are extracted. In a word, we shall find throughout all nature, that all what can be, is.

The same difference exists in the time of female gestation; some, as mares, carry their young eleven or twelve months; others, as women, cows, &c. nine months; others, as foxes, wolves, &c. five months; bitches, nine weeks; cats, six weeks; rabbits, thirty-onedays. Most birds come out of the egg at the end of twenty-one days; though some, as canary birds, hatch in thirteen or fourteen days. The variety is as great here as in every thing else relative to animals. The largest animals which produce only few, are those which go the longest with young; this still more confirms what we have already said, that the quantity of organic food is in proportion less in large than in small animals; for it is from the superfluity of the mother's food that the fœtus derives what is necessary to the growth and expansion of its parts, and since this expansion demands much more time in large than in small animals, it is a proof that the quantity of matter which contributes is not so abundant in the first as in the last.

There is, therefore, an infinite variety in animals, with respect to the time and manner of gestation, engendering, and bringing forth; and this variety is found even in the causes of generation; for although the general principle of production is this organic matter common to all that lives or vegetates, the manner in which the union is made, must have infinite combinations, which must all proceed from the source of new productions. My experimentsclearly demonstrate, that there are no pre-existing germs, and at the same time prove that the generation of animals and vegetables is not equivocal; there are, perhaps, as many beings, either living or vegetating, which are produced by the fortuitous assemblage of organic molecules, as by a constant and successive generation. It is to those productions we should apply the axiom of the ancients, "Corruptio unius, generatio alterius." The corruption and composition of animals and vegetables produce an infinite number of organized bodies; some, as those of the calmar, form only kinds of machines, which, although very simple, are exceedingly active; others, as the spermatic animalcules, seem by their motion, to imitate animals; others imitate vegetables by their manner of growing or extending; there are others, as those of blighted corn, which may be made to live and die alternately, and as often as we please; there are still others, even in great quantities, which are at first kinds of vegetables, afterwards become species of animals, then return again to vegetables, and so on alternately. There is a great appearance, that the more we shall observe this race of organized beings, the more we shall discovervarieties, always so much the more singular as they are the more remote from our sight, and from the varieties of other animals that have already become known to us.

For example, spurred barley, which is produced by an alteration or decomposition of the organic substance of the grain, is composed of an infinity of little organized bodies, like to eels. By infusing the grain for ten or twelve hours in water, we find them to have a remarkable twirling, and a slight progressive motion; when almost dry, they cease to move, but by adding fresh water their motion returns. The same effects may be produced for months, or even years; insomuch that we can make these little machines act as often and as long as we please without destroying them, or their losing any of their power or activity. Their threads will sometimes open, like the filaments of semen, and produce moving globules; we may therefore suppose them to be of the same nature, only more fixed and solid.

Eels, in paste made with flour, have no other origin than the union of the organic particles of the most essential parts of the grain: the first which appear are certainly not produced by many others; yet, althoughthey have not been engendered, they engender others. By cutting them with the point of a lancet, we may perceive small eels come from their bodies in great numbers; the body of the animal appears to be only a sheath or bag which contains a multitude of other little animals, which perhaps are themselves only sheaths of the same kind, in which the organic matter assimilates, and takes the form of eels.

There requires a great number of observations to be made to establish classes and races between such singular beings, which are at present so little known; there are some which may be regarded as real zoophytes, which vegetate, and at the same time appear to twirl and move like animals. There are some that at first appear to be animals, which afterwards join and form kinds of vegetables. A little attention to the decomposition of a grain of wheat infused in water will elucidate all I have asserted. I could add more examples, but I have related these only to point out the varieties there are in generation. There are certainly organized beings which we regard as animals, but which are not engendered by others of the same kind; thereare some which are only a kind of machines, whose action is limited to a certain effect, and which can act but once in such a certain time, as those in the calmar; and there are others, as we have just remarked, which we can cause to act as long and as often as we please. There are vegetating beings which produce animated bodies, as the filaments of the human seed, from whence the active globules spring, and which move by their own powers. In the corruption, fermentation, or rather the decomposition of animal and vegetable substances, there are organized bodies which are real animals, and can propagate their like, although they have not been so produced. The limits of these varieties are perhaps still greater than we can imagine. We may extend our ideas, and exert every effort to reduce the effects of Nature to certain points, and class her productions to certain classes, yet an infinite number of links will always escape us.

CHAPTER X.

OF THE FORMATION OF THE FŒTUS.

It appears to be clearly ascertained by the experiments of Verheyen, who in one of them found the seed of a bull in the matrix of a cow; and by those of Ruysch, Fallopius, Leeuwenhoek, and many others, who perceived the male semen in the uterus of women, and numberless other animals, that the seminal liquor of the male enters by some means into the matrix of the female. It is probable, that in the time of copulation the orifice of the matrix opens to receive the seminal liquor, but if that is not the case, the active and prolific substanceof this liquor, may penetrate the membranes of the matrix; for the seminal liquor being, as we have proved, almost all composed of organic molecules, which are in great motion, and extremely minute, they may pass across the coat of the closest membranes, and penetrate those of the matrix with the greatest facility.

What proves that the active part of this liquor may not only pass through the pores of the matrix, but even penetrate its substance, is the sudden change that immediately takes place after conception. The menses are suppressed, the matrix becomes softer, swells, and appears inflamed. All these alterations can only happen by the action of an external cause; by the penetration of some part of the seminal liquor into the substance even of the matrix. This penetration not only operates on the external surface of the matrix, but on all the other parts of which this viscera is composed, like that penetration by which nutrition and expansion is produced.

We shall be easily persuaded that it is so, when we consider that the matrix, during the time of gestation, not only augments in bulk but also in quantity of matter, and that it hasa kind of life or vegetation, which is continually increasing till the time of delivery; for if the matrix was only a pouch, a destined receptacle to receive the seed and contain the fœtus, it would extend and grow thin in proportion as the fœtus increased in size; but in reality the matrix not only extends in proportion as the fœtus grows larger, but receives at the same time a thickness and solidity. This augmentation is a real growth, like the expansion of the body in young animals, which can only be produced by the intimate penetration of the organic molecules analogous to the substance of the parts: and as this expansion of the matrix never happens but after impregnation, we cannot doubt its being produced by the liquor of the male, especially as the expansion takes place before the fœtus has sufficient bulk to dilate it.

It seems certain, by my experiments, that the female has a seminal liquor which commences to be formed in the testicles, and is completed in the glandular bodies: this liquor distills through the small holes, at the extremities of these bodies; and may, like that of the male, enter into the matrix in two different manners, either by these holes at the extremities,or through the membraneous coat of the matrix.

These seminal liquors are both extracts from all parts of the body, and in the mixture of them there is every thing necessary to form a certain number of males and females; and the more the animal abounds with this liquor, and the more that abounds with organic molecules, the greater is their number of young; as we have already remarked is the case with the small animals, and diminishes in the large.

But to pursue our subject with greater attention, we shall first examine the particular formation of the human fœtus, and afterwards return to the other animals. In the human species, as well as in large animals, the seminal liquors of the male and female do not contain a great abundance of organic molecules, and therefore seldom produce more than one at a time: the fœtus is a male, if the number of the organic molecules of the male predominates in the mixture, and a female if the contrary; and it resembles the father or the mother as they happen to abound in the mixture of the two liquors.

I conceive, therefore, that the seminal liquor of both are two matters equally activeand necessary for generation; and this I think is sufficiently proved by my experiments, since I have seen the same moving bodies in the one as the other. I perceived that the liquor of the male enters into the matrix, where it meets with that of the female: that they have a perfect analogy, and are both not only composed of similar parts by their form, but also in their motions and actions; as we have remarked inChap. VI.

By the mixture of these two liquors I conceive the activity of the organic molecules of each is stopped, and that the actions of one counterbalance that of the other, insomuch that each particle ceasing to move, remains in the place most analogous to itself, and that they will naturally take the same position, and will dispose themselves in the same order they held in the animal body; those that came from the head will arrange themselves in the head of the fœtus, those of the back the same, and so of every other part; consequently they will form a small organized being, in every thing like the animal from which they are extracted.

It must be observed that this mixture of organic molecules of the two sexes contains similarand different particles; the similar ones are those which have been extracted from every part common to both sexes. The different particles are those which have been extracted from the parts whereby the sexes are distinguished; thus there is, in this mixture, double the number of organic molecules to form the head, or the heart, or such other parts common to both, whereas there are only what are requisite to form the parts of the sex. Now the similar particles may act upon each other without being disordered, and collect together as if they had been extracted from the same body; but the dissimilar parts cannot act on each other, nor unite together, because they have not any relation; hence these particles will preserve their nature without mixture, and will fix of themselves the first, without the need of being penetrated by the others. Thus the molecules proceeding from the sexual parts will be the first fixed, and all the rest which are common to both, will afterwards fix indiscriminately, whether they are those of the male or female, and form an organized being which, in its sexual parts, will perfectly resemble its father, if it is a male, and its mother if a female; butwhich may resemble one another, or both, in all the other parts of the body.

It seems to me that if this was well understood, we shall in a great measure be enabled to answer the objections made to the sentiments pf Aristotle, and which might also be advanced against this system. The question is, Why each individual, male and female, does not produce of itself an animal of its own sex? It must be acknowledged this question seems to carry weight with it; but having reflected a long time on this subject I think I have found an answer, and which I shall endeavour to explain.

It is certainly evident, from what we have said in the preceding chapters, and the experiments we have described, that reproduction is effected by the union of organic molecules returned from each part of the body of the animal, or vegetable, into one or many common reservoirs; and that they are the same molecules which serve for nutriment and expansion of the body. This appears to me to have been so clearly proved, that I apprehend no scruple can remain as to the foundation of the theory; but I admit there may be some reason to ask, Why each animal and vegetable does not produce itsown likeness, since each individual returns from every part of its body, and collects in a common reservoir, all the organic molecules necessary for the formation of a small organized being? Why then is not this organized being formed? and why, in almost every animal, is a mixture of the liquors of the two sexes required to produce an animal? If I content myself with answering, that in almost all vegetables, and all kinds of animals which multiply by cutting, that it appears the design of Nature that each individual should increase its own species, and that we must regard as an exception to this rule, the use which is made of the sexes in other kind of animals; it may be said, that the exception is more universal than the rule itself. This difficulty will be very little weakened, if we were to say, that each individual perhaps would produce its like, if it had proper organs, and contained the necessary matter towards the nutriment of the embryo; because females have both this matter, and organs, and yet do not produce either male or female fœtus without the intervention of the male; which intervention of sexes in all animals is essential and absolutely necessary.

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