It was a great improvement in our zoological investigations when the differences in their relations, according to the various degrees of affinity or analogy which exist between animals, were pointed out, and successively better understood. In earlier times, zoologists madeno distinction between the different relations which existed among animals. Affinity and analogy, so dissimilar in their essential characters, were constantly mistaken one for the other; and upon the peculiarities which struck the observer most at first sight, animals were brought together, sometimes upon the ground of true affinity, sometimes, also, upon the ground of close analogy; and though comparative anatomy did put the mistakes arising from such confusion right, by showing that external appearances were sometimes deceptive, and that a more intimate knowledge of internal structure was necessary fully to understand the real relations between animals, there remained, nevertheless, a degree of uncertainty in many[N18]cases, as long as the principles of affinities and of analogies were not fully distinguished. Every naturalist now knows that true relationship—affinity—depends upon a unity in structure, however diversified the forms may be under which their fundamental structure is displayed. For instance, the affinity of whales and the other mammalia was not understood before it was shown that, under the form of fishes, these animals had truly the same structure as the highestvertebrata.
Again, the forms ofcetaceaexemplify the analogy there is between whales and fishes. They arerelatedto mammalia; they areanalogous[N19]to fishes; they bear close affinity to the mammals which nurse their young with milk; they have rather close analogy to the gill-breathing fishes.
Since the fossil animals which have existed during former periods upon the surface of our globe, and which have successively peopled the ocean and the dry land, have been more carefully studied than they were at the beginning of these investigations; since they are no longer considered as mere curiosities, but as the earlier representatives of an order of things which has been gradually and successively developed throughout the history of our globe, facts have been brought to light which now require a very careful examination, and will lead to a more complete understanding of the various relations which exist between these extinct types and those which still continue to live in our days. Upon close comparison of these facts, I have been led to distinguish two sorts of relations between the extinct animals, and those of our days, which seem to me to have been either overlooked or not sufficiently distinguished. Indeed, the general results derived from Palæontological investigations, seem scarcely to have gone beyond showing that the animals of former ages are specifically and frequently also generically distinct from those of the present creation; and also to establish certain graduation between them, agreeing more or less with the degree of perfection which we recognise between the living animals according to their structure.
It is now pretty generally understood that fishes, which rank lowest among theVertebrata, have existed alone during the oldest periods; that the reptiles which, in the gradation of structure, rank nextabove them, have followed at a later period; that still later the birds, which, according to their anatomy, rank above reptiles, have next made their appearance; and that mammalia, which stand highest, have been introduced last, and even among these the lower families seem to have been more numerous, before the higher ones prevailed over them. Man, at last, has been created, only after all other types had acquired their full development. These facts which, in such generality are fully exemplified in every country in the order of succession of the different fossil characteristics of the various geological deposits, shew plainly that a gradation really exists in this succession, and constitutes one of the most prominent characters of the development of the animal kingdom as a whole.
If we investigate, however, this gradation, and the order of succession of animals more closely, we cannot but be struck with the different relations which exist between the fossils and the living animals. Many extinct types have been pointed out as characteristic of different geological periods, which combine, as it were, peculiarities which at present are found separately in different families of animals.
I may mention as such, theIchthyosaur[N20], with their fish-like vertebræ, their dolphin or porpoise-like general form, and several special characters reminding us of their close relation to the Crocodilian reptiles; thus combining characters of different classes in the most extraordinary manner.
Again, thePterodactyli, in which reptilian characters are combined with peculiarities reminding us both of birds and bats.
Again, the large carnivorous[N21]fishes of the coal period, combining peculiarities of theSaurians, with true fish characters; and so on.
These relations are of an entirely different kind from those which I have pointed out between some of the older fossils and the early stage of growth of the living representatives of the same families.
For instance, the fossil fishes with a heterocercal tail, found below the new red sandstone, down to the lowest deposits, reminds us of the peculiar termination of the vertebral column in all fish embryos of species living in the present period, to whatever family they may belong, indicating a similarity of structure in the oldest representative of this class, with the earliest condition of the germs of those animals in our days.
Let us now examine whether we can properly understand the bearings of these relations, and the meaning of such differences.
In the first place, I have mentioned the gradual progress, which is observed in the succession of the different classes ofVertebrata. This progress is exemplified by a series of types which differ from each other, but which shew, when arranged in a series, a gradation which agrees in general with the structural gradation, which we may establish upon anatomical evidence. For instance, the salamanders, with their various forms, rank below the tailless[N22]Batrachians.
And where we have a succession of those animals in the tertiarydeposits as they occur in various parts of Europe, we may fairly say that the fossils form, in their succession, a series of progressive types.
Another example may perhaps illustrate the point more fully. Theorthoceraof the oldest periods precede the curved lituites, which, in their turn, are followed by the circumvolute[N23]nautilus. Here, again, we have a natural gradation of a series of progressive types. Again, amongcrinoids, we find, in the older deposits, a variety of species resting upon a stem, while free crinoids begin to appear only during the secondary deposit and prevail, in the present creation, over those attached to the soil. Here, again, we have a series of progressive types developed successively, which are apparently independent of each other and seem to bear no other relation to each than that arising from the general character of the group to which they belong. Such types exemplify simply in the groups to which they belong, a real progress in the successive development of the peculiarities which characterise them as natural divisions among animals. Such forms I shall callProgressive Types.
The relations, however, which are exemplified in the oldest fishes, in the ichthyosaurians, in the pterodactyls or in the megalosaurians, seem to me to be clearly of a different character, and to differ from simple progressive types, inasmuch as those which appear earlier, combine peculiarities which, at a later period, appear separately in distinct forms. For instance, the reptilian characters which we recognise in the sauroid fishes, are developed at a later period in animals no longer belonging to the class of fishes, but constituting by themselves new types, provided with additional peculiarities which separate them fully from the fishes in general, as well as from those fishes in which we recognise some relation to reptiles during a period when no reptile existed.
Again, the ichthyosaurians, though true reptiles appearing long after fishes had been called into existence, and during an early period of the history of the reptiles, still shew their relation to fishes by the character of their vertebral column, and foreshadow, as it were, in their form, the cetacea of later ages, as well as many forms of the gigantic saurians of the secondary period. The same may be said of the pterodactyls, which are also true reptiles, but, in which the anterior extremity foreshadow peculiarities characteristic of birds and bats. Such types I shall callProphetic Types.
To an analytic mind the examination of the peculiarities of such animals may foretell[N24]a higher progress of development, carried out in real existence, only during a later period, even if he had never seen the later ones; for in such types the germs of a future development may be recognised, and upon close examination, truly referred to the peculiarities of other higher groups, even if the intermediate links remained unknown, which, however, as the matter now stands,can leave no doubt in our mind that these prophetic types really foreshadowed that diversity of forms which has been created since they have gone by. We may also say that these prophetic types lay before us the course of thoughts which has been carried out in the plan of creation by the Supreme intelligence, who called them into existence in rich order of succession, and in so diversified relations. The recognition of this prophetic character of certain types of extinct animals is not only important in a philosophical point of view; I have no doubt it will ultimately and rapidly lead to a better, fuller, higher, and deeper understanding of the various relations which exist between animals. Let me at once point to some of these relations which might never have been understood but for this appreciation.
Among Crinoids, we have not only progressive types, as I have already quoted, but we have also prophetic ones. The Cystidæ are truly prophetic of the Echini proper. I may only mention the genus Echinocrinus to shew the link.
The Pentremites, again, are the prophetic type foreshadowing the star-fishes. And often in subordinate groups we may find such close relations between genera of the same minor divisions; such, for instance, as the genus Encrinus, in which the genera Apiocrinus and Pentacrinus, are simultaneously foreshadowed. Perhaps, in this case, a distinction might be introduced between truly prophetic types and synthetic types, in which the characters of later groups are rather more combined than really foreshadowed.
As for the relation between older types and the embryos of the living representatives of the same families which are so extensively observed in almost all groups of the animal kingdom, which have existed during earlier periods, it may best be expressed if we call those fossils which exemplify, in full grown animals, forms which exist at present only in the earliest stages of growth of our living animals,Embryonic Types, in counterdistinction from the progressive types, and from the prophetic types. These embryonic types may be purely such, or they may be at the same time either progressive types, or even prophetic types. I shall call purely embryonic types those in which we recognise peculiarities characteristic of the embryo of the same family. For instance, the older Sauroids, which have the upper lobe of the tail prolonged, or the common Crinoids provided with a stem, which resemble the young Comatulæ,&c.,&c.I shall distinguish, as progressive embryonic types, those in which we recognise simultaneously a relation to the embryo of the same family, when they form besides a link in the natural chain of progressive development. Such, for instance, as the oldest Salamanders, or the earliest Sirenoid Pachyderm. Finally, I shall call prophetic embryonic types those in which we have embryonic characters, combined with the peculiarities which stamp the type as a prophetic one,such, for instance, as the Echinoid and Asteroid Crinoids of the former ages.
The fact that these different types may thus present complications of their character, or appear more or less pure and typical, goes further to shew how deeply diversified the plan of creation is, and how many relations should be simultaneously understood before we are prepared to have a full insight into the plan of creation. There we see one type forming simply, and alone, the first link of a progressive series. There we see another which foreshadows types, which appear isolate afterwards. There we see a third, which, in its full development, exemplifies a state which is transient only in higher representatives of the same family. And then, again, we see these different relations running into each other, and reminding us that, however difficult it may be for us to see at one glance all this diversity of relations, there is, notwithstanding, an intelligence which not only conceived these various combinations, but called them into real existence in a long succession of ages.—L. Agassiz in the American Association for the Advancement of Science, August 1849.
At the recent meeting of the Association for the Advancement of Science, an announcement was made, which, if it is found to be correct, will be regarded as relating to one of the most important discoveries which have been made in astronomy for years. It is no less than a new law of the solar system, closely resembling those of Kepler, which form the groundwork of many of the problems of astronomy. Mr S. C. Walker read to the Association a letter from Mr Daniel Kirkwood, of Pottsville,Pa., the discoverer of this new law, from which we make some extracts, omitting all that refers to the higher branches of mathematics.
“While we have in the law of Kepler a bond of mutual relationship between the planets, as regards their revolutions around the sun, it is remarkable that no law regulating their rotations on their axes has ever been discovered. For several years I have had little doubt of the existence of such a law in nature, and have been engaged, as circumstances would permit, in attempting its development. I have at length arrived at results, which, if they do not justify me in announcing the solution of this important and interesting problem, must at least be regarded as astonishing coincidences.”
After stating some equations, he gives the following tables as the data on which he has proceeded:—
From these data he deduces the following law:—“The square of the number of a primary planet's days in its year, is as the cube of the diameter of its sphere of attraction in the nebular hypothesis.”
"The points of equal attraction between the planets severally (when in conjunction), are situated as follows:—
"It will be seen from the above, that the diameter of the earth's sphere of attraction is 49,864,000 miles. Hence the diameters of the respective spheres of attraction of the other planets, according to my empirical[N25]law, will be found to be as follows:—
“The volumes of the sphere of attraction of Venus, Mars, and Saturn in this table, correspond with those obtained from the preceding one; that of Mars extending 61,000,000 miles beyond his orbit, or to the distance of 206,000,000 miles from the sun. This is about 2,000,000 or 3,000,000 miles less than the mean distance of Flora, the nearest discovered asteroid. That of Mercury extends about 11,000,000 miles within the orbit; consequently, if there be an undiscovered planet interior to Mercury, its distance from the Sun, according to my hypothesis, must be less than 26,000,000 miles. Jupiter's sphere of attraction extends only about 200,000,000 of miles within his orbit, and leaving 89,000,000 miles for the asteroids. It is only in the most distant portion of this space, where small bodies would be likely to be detected, that none have yet been discovered.”
Mr Kirkwood then modestly concludes:—
“The foregoing is submitted to your inspection with much diffidence. An author, you know, can hardly be expected to form a proper estimate of his own performance. When it is considered, however, that my formula involves the distances, masses, annual revolutions, and axial rotations of all the primary planets in the system, I must confess I find it difficult to resist the conclusion, that the law is founded in nature.”
After this letter had been read, Mr Walker said, that, induced by the importance of the subject, he had at once proceeded to verify the data and conclusions of Mr Kirkwood, and had found that there was nothing in them requiring modification, except, perhaps, the substitution of some more recent values for the masses of Mercury and Uranus. This theory and that of Laplace, with reference to nebulæ, mutually strengthen each other; although the latter has been a mere supposition, while the former rests upon a mathematical basis. In a later letter, which was also read, Mr Kirkwood says that he has pursued this subject for the last ten years, it having been first suggested to him by the nebular hypothesis, which he thought could be established by some law of rotation.
Mr Walker then entered into a lengthened examination of the data on which the law rests, and seemed to come to the conclusion, that, as far as we know at present, everything is in favour of the truth of the law, except that it requires the assumption of another planet between Jupiter and Mars.
Mr Walker closed his examination by saying, "We may, therefore, conclude, that,whether Kirkwood's analogy is or is not the expression of a physical law, it is, at least, that of a physical fact in the mechanism of the universe. The quantity on which the analogy is based has such immediate dependence upon the nebular hypothesis, that it lends strength to the latter, and gives new plausibility to the presumption that this, also, is a fact in the past history of the solar system.
"Such, then, is the present state of the question. Thirty-six elements of nine planets (four being hypothetical) appear to harmonize with Kirkwood's analogy in all the four fundamental equations of condition for each planet.
"To suppose that so many independent variable quantities should harmonize together by accident, is a more strained construction of the premises than the frank admission that they follow a law of nature.
"If, in the course of time, the hypotheses of Laplace and Kirkwood should be found to be the laws of nature, they will throw new light on the internal organization of the planets in their present, and in any more primitive, state through which they may have passed.
"For instance, we may compute the distance from the centre atwhich any planet must have received its projectile force, in order to produce, at the same time, its double movement of translation and rotation.
"If the planet, in a more primitive state, existed in the form of a ring revolving round the Sun, having its present orbit for that of the centre of gravity of the ring, the momentum of rotation must, by virtue of the principle of conservation of movement, have existed in some form in the ring. It is easy to perceive that this momentum is precisely the amount which must be distributed among the particles of the ring, in order to preserve to all the condition of dynamical equilibrium, while those of each generating surface of the ring were wheeling round with the same angular velocity.
"If the planets have really passed from the shape of a revolving ring to their present state, the prevalence of Kirkwood's analogy shews a nice adaptation of parts in every stage of the transition.
"If the primitive quantity of coloric (free and latent) had undergone a very great change beyond that now indicated in the cooling of their crusts; if the primitive quantity of movement of rotation had been different from its actual value for any planet; if the law of elasticity of particles for a given temperature and distance from each other varied from one planet to another in the primitive or present state; in either of these cases, the analogy of Kirkwood might have failed. As it is, no such failure is noticed; we are authorised, therefore, to conclude, that the primitive quantity of coloric, the law of elasticity, the quantity of movement of rotation, the past and present radii of percussion, the primitive diameter of the generating surface of the rings, and the present dimensions and density of the planets, have been regulated by a general law, which has fulfilled for all of them the four fundamental conditions of Kirkwood's hypothesis[N26].
“We may extend the nebular hypothesis and Kirkwood's analogy to the secondary system. If they are laws of nature, they must apply to both. In the secondary systems, the day and month are the same. This fact has remained hitherto unexplained. Lagrange shewed that if these values were once nearly equal, a libration sets in round a state of perfect equality; but he offered no conjecture as to the cause of the primitive equality. On the nebular and Kirkwood's hypothesis, it would only be necessary that, upon the breaking up of the ring, the primitive diameter of the generating figure and law of relative density of layers should be preserved.”
Professor Peirce, whose opinions will probably be regarded as of more value on such a subject than that of any other man in this country,—especially since his successful discussion with Leverrier,—remarked, that Kirkwood's analogy was the only discovery of the kind since Kepler's time that approached near to the character of his three physical laws. Bode's law, so called, was at best only an imperfect analogy. Kirkwood's analogy was more comprehensive, and more in harmony with the known elements of the system. Thediameter of the sphere of attraction, a fundamental element in this analogy, now for the first time gave an appearance of reality to Laplace's nebular hypothesis which it never had before. The positive testimony in its favour would now outweigh the former negative evidence in the case, however strong it may have been. It follows at least from Kirkwood's analogy, that the planets were dependent upon each other, and therefore connected in their origin, whatever may have been the form of the connection, whether that of the nebular hypothesis, or some other not yet imagined.
At a later period of the meeting, M. B. A. Gould junior, stated that he had gone through the necessary calculations, using different quantities, and had come to the same conclusions as Mr Walker. He expressed his opinion, that at some future day the world will“speak of Kepler and Kirkwood as the discoverers of great planetary laws.”
The members generally expressed the opinion, that Laplace's nebular hypothesis, from its furnishing one of the elements of Kirkwood's law, may now be regarded as an established fact in the past history of the solar system.—American Annual of Scientific Discovery,p.335.
Note.—Such, at least, is rather a representation of American opinions than of our own. We are inclined to compare it more with Bode's law than with Kepler's. The former is a mere arithmetical accident, applying indifferently well to a portion only of the planets, and having nothing of reason to advance for its establishment. The latter are essential parts of mechanics and gravitation, and precisely and perfectly, and necessarily true, not only in every part of the solar system, but through the whole universe.
The fact of axial rotations being the groundwork of Kirkwood's analogy seems fatal to it, for gravitation takes no more account of the time of rotation of a planet than it does of specific gravity; all calculations of the movement of the body in space are equally independent of the one and the other.
Under these circumstances, the degree of accuracy with which it may be found to apply is the only saving clause. Messrs Walker and Gould investigating the subject independently, and with better constants of mass and distance than Kirkwood had been able to procure, declare that it appearsperfectly! We are sorry that the late hour at which we have received this paper has prevented us either from giving it in full, or from testing the theory rigidly.
It will be observed that, according to Kirkwood's theory, in order to compute the time of axial rotations of any planet, it is necessary to have its mass and mean distance, together with the same quantities for the planets on either side of it. Now, these quantities are only obtainable for Venus, the Earth, Saturn, and Uranus (a planet being lost between Mars and Jupiter); and the rotation of Uranusnot having been obtained as yet, there remains only the three first by which the theory can be tested.
In a preliminary calculation which we have instituted, we do not find the results so accordant as we had been led to expect, but still sufficiently so to give a certain probability of the approach to truth, in a case where the quantity had not been observed.
Viewed in this light, some very interesting results are obtained.1st, The idea entertained by Bianchini and other observers, that the rotation of Venus is nearly 24 times as long as hitherto supposed, is utterly untenable.
2d, The time of rotation of Uranus, a quantity never yet observed (but doubtless capable of being observed by a telescope of Lord Rosse's calibre,removed to a table-land in a tropical country) is given; and appears so very different from any other yet observed, especially so from those of its neighbours Saturn and Jupiter, being = 1·396779, earth's = 0·997270 (sidereal rotation in mean solar days.)
3d, Knowing the rotations of Jupiter and Mars, we may supply, by using the analogy conversely, thediameters of their spheres of attraction, and thus get at the elements of the lost planet between Mars and Jupiter, and these appear[N36]to be:—mean distance = 2·9085111 (earth unity), mass in terms of Sun 1/1353240, sidereal rotation in earth's mean solar days 2·406104, and diameter of sphere of attraction 0·830951, in terms of earth's distance. The size is thus a little larger than Mars. The slowness of rotation is remarkable, especially in the case of a planet which is supposed since to have burst into pieces: the Americans have called it Kirkwood.
P. S.
METEOROLOGY.
1.Use of Coloured Glasses to assist the View in Fogs.—M. Lavini of Turin, in a letter to the editor ofL'Institutat Paris, makes the following curious observation, which, if confirmed, may prove to be of great importance:—“When there is a fog between two corresponding stations, so that the one station can with difficulty be seen from the other, if the observer passes a coloured glass between his eye and the eye-piece of his telescope, the effect of the fog is very sensibly diminished, so that frequently the signals from the other station can be very plainly perceived; when, without the coloured glass, even the station itself is invisible. The different colours do not all produce this effect in the same degree, the red seeming to be the best. Those who have good sight prefer the dark-red, whilethose who are short-sighted like the light-red better. The explanation of this effect seems to depend upon the fact, that the white colour of the fog strikes too powerfully upon the organ of sight, especially if the glass have a somewhat large field. But by the insertion of the coloured glass, the intensity of the light is much diminished by the interception of a part of the rays, and the observer's eye is less wearied, and, consequently, distinguishes better the outlines of the object observed.”
2.Ozone.—Chemists are not yet fully agreed concerning the nature or production of this singular substance, ozone. To Schonbein and Williamson we are indebted for most of our knowledge concerning it. The latter has supposed it to be a compound of oxygen and hydrogen, from the fact, that, when the ozone completely freed from moisture was passed over ignited copper, water was produced. De la Rive produced it by passing a current of electricity through pure dry oxygen gas contained in a receiver. It is also obtained in large quantities by passing oxygen gas over moistened phosphorous, and afterwards drying it. Thus prepared, it is a powerful chemical agent, possesses bleaching properties, oxidises the metals with rapidity, and destroys India-rubber. The hydrogen acids of sulphur are decomposed by it, water being formed by uniting with the hydrogen of the acid, and sulphur being set free. Professor Horsford has observed that ozone, subjected to a heat of 130° Fah., entirely loses its properties. Ozone, like chlorine, precipitates iodine, colouring a solution of iodide of potassium, and starch a deep blue colour. The peculiar smell, prevalent in the vicinity of objects struck by lightning, as well as that occasioned by the excitation of an electrical machine, and by the striking of two pieces of silica together, it is believed to be occasioned by ozone.—Editors.—Annual of Scientific Discovery,p.219.
Method of Determining the Amount of Ozone in the Atmosphere.—At the meeting of the American Association, an instrument for determining the relative quantity of ozone in the air was presented by Professor Horsford. It consisted of a tube, containing at one end a plug of asbestus, moistened with a solution of iodide of potassium and starch. This plug within the tube, attached to an aspirator, would, as air passed over it, become blue. If much water flowed from the aspirator, and of course much air flowed over the asbestus before it became blue, the quantity of ozone indicated would be small. If but little water flowed (and this could be measured), the quantity of ozone indicated would be greater. The quantities of ozone would be inversely as the volumes of air passing through the tube before blueness is produced.—Annual of Scientific Discovery,p.219.
HYDROGRAPHY.
3.On the Phenomena of the Rise and Fall of the Waters of the Northern Lakes of America.—At a meeting of the American Academy, February 1849, Mr Foster, of the United States Mineral Survey in the North-west Territory, presented the result of some observations, undertaken with a view of determining whether the waters of the northern lakes are subject to any movements corresponding to tidal action. The result of these observations had convinced him that these waters do not rise and fall at stated periods, corresponding to the ebb and flow of the tide, but are subject to extraordinary risings, which are independent of the influence of the sun and moon. These risings attracted the attention of the earliestvoyageursin these regions. Charlevoix, who traversed the lakes nearly a century ago, says, in reference to Lake Ontario:—“I observed that in this lake there is a sort of reflux and flux almost instantaneous; the rocks near the banks being covered with water, and uncovered again several times in the space of a quarter of an hour, even if the surface of the lake was very calm, with scarce a breath of air. After reflecting some time on this appearance,I imagined it was owing to springs at the bottom of the lake, and to the shock of their currents with those of the rivers which fall into them from all sides, and thus produce those intermitting motions.”The same movements were noticed by Mackenzie in 1789; by an expedition under Colonel Bradstreet in 1764; on Lake Erie in 1823, and at various later periods. In the summer of 1834, an extraordinary retrocession of the waters of Lake Superior took place at the outlet of Sault St Marie. The river at this place is nearly a mile wide, and in the distance of a mile falls 18·5 feet. The phenomena occurred about noon. The day was calm, but cloudy. The water retired suddenly, leaving the bed of the river bare, except for a distance of thirty rods, and remained so for nearly an hour. Persons went out and caught fish in pools formed in the depressions of the rocks. The return of the waters is represented as having been very grand. They came down like an immense surge, and so sudden was it, that those engaged in catching fish had barely time to escape being overwhelmed. In the summer of 1847, on one occasion the water rose and fell at intervals of about fifteen minutes during an entire afternoon. The variation was from twelve to twenty inches, the day being calm and clear; but the barometer was falling. Before the expiration of forty-eight hours, a violent gale set in. At Copper harbour, the ebb and flow of the water through narrow inlets and estuaries has been repeatedly noticed when there was not a breath of wind on the lake. Similar phenomena occur on several of the Swiss lakes. Professor Mather, who observed the barometer at Copper harbour during one of these fluctuations, remarks:—“As a general thing, fluctuations in the barometer accompanied fluctuations in the level of the water; but sometimesthe water-level varied rapidly in the harbour, while no such variations occurred in the barometer at the place of observation.”
As a general rule, these variations in the water-level indicate the approach of a storm, or a disturbed state of the atmosphere. The barometer is not sufficiently sensitive to indicate the sudden elevations and depressions, recurring, as they often do, at intervals of ten or twelve minutes; and the result of observations at such time may, in some degree, be regarded as negative. Besides, it may not unfrequently happen, that, while effects are witnessed at the place of observation, the cause which produced them may be so far removed as not to influence the barometer. We are, therefore, led to infer that these phenomena result, not from the prevalence of the winds acting on the water, accumulating it at one point and depressing it at others, but from sudden and local changes in the pressure of the atmosphere, giving rise to a series of barometric waves. The water, conforming to the laws which govern two fluids thus relatively situated, would accumulate where the pressure was the least, and be displaced where it was the greatest. It has been remarked by De la Beche, that a sudden impulse given to the particles of water, either by a suddenly increased or diminished pressure, would cause a perpendicular rise or fall, in the manner of a wave, beyond the height or depth strictly due to the mere weight itself. The difference in the specific gravity of the water of the lakes and the ocean may cause these changes to be more marked in the former than in the latter.—American Annual of Scientific Discovery,p.245.
4.Water Thermometer.—Lieut. Maury states that he has been very much assisted in developing his theory of winds and currents by means of the thermometer used by some vessels for determining the temperature of the water. It was by means of these observations on the temperature of the water that he was enabled to prove that, off the shores of South America, between the parallels of 35° and 40° south, there is a region of the ocean in which the temperature is as high as that of our own Gulf stream, while in the middle of the ocean, and between the same parallels, the temperature of the water is not so great by 22°. Now, this very region is noted for its gales, being the most stormy that the as yet incomplete charts of the South Atlantic indicate. Lieut. Maury says, however, that very few navigators make use of the water thermometer, so that he has experienced some inconvenience in his undertaking. He is the more surprised at this, from the fact that New York owes much of her commercial importance to a discovery that was made by this thermometer. At the time when Dr Franklin discovered the Gulf Stream, Charleston had more foreign trade than New York and all the New England States together. Charleston was then the half-way house between New and Old England. When a vessel, in attempting to enter the Delaware or Sandy Hook, met a north-west gale or snow storm, as at certain seasons she is apt to do, instead ofrunning off for a few hours into the Gulf Stream to thaw and get warm, as she now does, she used to put off for Charleston or the West Indies, and there remained till the return of spring before making another attempt. A beautiful instance this of the importance and bearings of a single fact, elicited by science from the works of nature.—Annual of Scientific Discovery,p.160.
5.On the Falls of Niagara.—If we follow the chasm cut by the Niagara river, down to Lake Ontario, we have a succession of strata coming to the surface of various character and formation. These strata dip south-west or towards the Falls, so that, in their progress to their present position, the Falls have had a bed of very various consistency. Some of these strata, as the shales and medina sandstone, are very soft, and, when they formed the edge of the Fall, it probably had the character of rapids; but, wherever it comes to an edge of hard rock, with softer rock-beds below, the softer beds, crumbling away, leave a shelf projecting above, and then the fall is perpendicular. Such is the case at present; the hard Niagara limestone overhangs intablesthe soft shales underneath, which at last are worn away to such an extent as to undermine the superincumbent rocks. Such was also the case at Queenston, where the Clinton group formed the edge, with the medina sandstone below. This process has continued from the time when the Niagara fell directly into Lake Ontario to the present time, and will continue so long as there are soft beds underneath hard ones; but, from the inclination of the strata, this will not always be the case. A time will come when the rock below will also be hard. Then, probably, the Falls will be nearly stationary, and may lose much of their beauty from the wearing away of the edge rendering it an inclined plane. I do not think the waters of Lake Erie will ever fall into Lake Ontario without any intermediate cascade. The Niagara shales are so extensive that possibly, at some future time, the river below the cascade may be enlarged into a lake, and thus the force of the falling water diminished; but the whole process is so slow, that no accurate calculations can be made. The Falls were probably larger, and stationary for a longer time at the“Whirlpool”than anywhere else. At that point there was no division of the cataract, but at the“Devil's Hole”there are indications of a lateral fall, probably similar to what is now called the American Fall. At the Whirlpool, the rocks are still united beneath the water, shewing that they were once continuous above its surface also.[89]—Agassiz on Lake Superior,p.15.
6.On the Existence of Manganese in Water.—At a meeting of the American Academy, in January 1849, Dr Charles T. Jacksonstated that he had discovered the presence of manganese in the water of streams, lakes,&c., almost universally. He detected it in water from the middle of Lake Superior, in Cochituate water, and in water from various sources. It has usually been regarded as iron in previous analyses. He considered the observation as having an important bearing in accounting for the deposits of bog manganese at the outlets of ponds, lakes, and in bogs, as well as for the source of the oxide of manganese in the blood.—Annual of Scientific Discovery,p.202.
On the Presence of Organic Matter in Water.—The following facts relative to the presence of organic matter in water were presented to the British Association, by Professor Forchhammer, as the result of extended observations on the water, near Copenhagen.
1st, The quantity of organic matter in water is greatest in summer.2d, It disappears, for the most part, as soon as the water freezes.3d, Its quantity is diminished by rain.4th, Its quantity is diminished if the water has to run a long way in open channels. The hypermanganate of potash or soda is recommended by the Professor as a most excellent test for the presence of organic matter in water.
7.Arsenic in Chalybeate Springs.—Since the discovery of arsenic in the deposits from certain chalybeate springs, it has been asked whether the poisonous properties of this substance are not neutralized by the state in which it is found. M. Lassaigne has finished a series of experiments connected with this subject, for the purpose of ascertaining the proportion of arsenic contained, in what state of combination it exists, and the nature of the action which these arseniferous deposits exert in the animal economy. The following are M. Lassaigne's conclusions:—1. In the natural deposits of the mineral waters of Wattviller, arsenic exists to the amount of 2·8 per cent. 2. A portion of these deposits, representing 1·76 grains of arsenic acid, or 1·14 grains of arsenic, produced no effect upon the health of a dog. 3. This non-action shews that the poisonous property of the arsenic is destroyed by its combination with the peroxide of iron, and thus confirms what has been before asserted, that peroxide of iron, by combining with arsenious[N27]and arsenic acid, destroys their poisonous properties, and consequently becomes an antidote for them.
[89]The data on which these and the previous remarks on the geology of the Falls are founded, are derived from Professor James Hall's investigations in the New York State Survey.
A.
GEOLOGY.
8.The Coal Formation of America.—The coal regions of America are, from the explorations which have thus far been made, supposed to be divided into three principal masses; the great central tract, extending from Tuscaloosa, Alabama, to the west of Pennsylvania, and being apparently continued to New Brunswick and Nova[N28]Scotia; the second tract strikes north-westward from Kentucky, crosses the Ohio, and stretches through Illinois to the Mississippi River; a thirdregion, smaller than the others, lies between the three great lakes—Erie, Huron, and Michigan. Competent geologists affirm that, from a comparison of the coal strata of contiguous basins, these are no more than detached parts of a once continuous deposit.
The extent of this enormous coal field is, in length, from north-east to south-west, more than 720 miles, and its greatest breadth about 180 miles; its area, upon a moderate calculation, amounts to 63,000 square miles! In addition to these, there are several detached tracts of anthracite in Eastern Pennsylvania, which form some of the most remarkable coal tracts in the world. They occupy an area of about 200 square miles.
The strata which constitute this vast deposit comprehend nearly all the known varieties of coal, from the dryest and most compact anthracite to the most fusible and combustible common coal. One of the most remarkable features of these coal-seams is their prodigious bulk. The great bed of Pittsburgh[N29], extending nearly the entire length of the Monongahela River, has been traced through a great elliptic area, of nearly 225 miles in its longest diameter, and of the maximum breadth of about 100 miles, the superficial extent being 14,000 square miles, the thickness of the bed diminishing gradually from 12 or 14 feet to 2 feet. In 1847 the anthracite coal regions of Pennsylvania furnished 3,000,000 tons, and 11,439 vessels cleared from Philadelphia in that year, loaded with the article. The produce in 1848 and the present year, is of course larger.
The bituminous coal area of the United States is 133,132 square miles, or one 17th part of the whole. The bituminous coal area of British America is 18,000 square miles, or one 45th part; Great Britain, 8139 square miles; Spain, 3408 square miles, or one 52d part; France, 1719 square miles, or one 118th part; and Belgium, 518 square miles, or one 122d part. The area of the Pennsylvania anthracite coal formations is put down at 437 square miles; and that of Great Britain and Ireland anthracite and culm, at 3720 square miles. The anthracite coal of Great Britain and Ireland, however, is not nearly so valuable an article of fuel as the anthracite coal of Pennsylvania, nor does a given area yield so much as the latter.—New York Express.American Annual of Scientific Discovery,p.271.
9.River Terraces of the Connecticut Valley.—At the meeting of the American Association in August, President Hitchcock of Amherst College, read a paper“On the River Terraces of the Connecticut Valley, and on the Erosions of the Earth's Surface.”He stated that his paper must be considered as containing a few facts and suggestions and not a finished theory. He has examined the valley from its mouth to Turner's Falls, and carefully measured the heights of the terraces. "As you approach the river you find plains of sand, gravel, or loam, terminated by a slope sometimes as steep as 35°, and a second plain, then another slope and another plain,and so on, sometimes to a great number. I find that these terraces occur in successive basins, formed by the approaches of the mountains upon the banks at intervals. Sometimes the basin will be 15 or 20 miles in width, but usually much narrower; and it is upon the margins of these basins that the terraces are formed. I have rarely found terraces more than 200 feet above the river, which would be in Massachusetts, about 300 feet above the ocean, and at Hanover,N.H.,[N30]about 560 feet. Nowhere do they exist along any river, unless that river has basins. As to the materials of which they are formed they appear exceedingly artificial. The outer or highest terrace is generally composed of coarser materials than the inner ones. They are all composed of materials which are worn from the rocks, but the outer terrace oftener is full of pebbles, some of them as large as 12 inches, while the materials of the inner seem reduced to an impalpable powder, like the soil of a meadow which is overflowed during high water. Whence did these materials originate? The materials were first worn from solid rocks, and afterwards brought into these valleys. The outer terrace appears to have been often in part the result of the drift agency. Afterwards, the river agency sorted the materials, and gave them a level surface, the successive basins having at that time barriers. The inner terrace appears to have been, at least in its upper part, the result of deposition from the river itself.
“I will now mention a few facts which I have observed. The terraces do not generally agree in height upon the opposite sides of the valley. The higher ones oftener agree, perhaps, than the lower ones. If formed, as I suppose, from the rivers, we should expect this. The terraces slope downwards in the direction of the stream. The same terrace which, near South Hadley, is 190 feet above the river, slopes until, at East Hartford, it is only 40 feet above the river, thus sloping 150 feet more than the slope of the river itself, in a distance of 40 or 50 miles. This shows that they could not have been formed by the sea or by a lake, for they would then have been horizontal. The greatest number of terraces observed is eight or nine. Generally there are but two or three.”President Hitchcock then gives his view of the precise mode in which these terraces were formed, illustrating them by references to other parts of our country, and concludes by a notice of the erosions of the earth's surface.—Annual of Scientific Discovery, 1850,p.229.
ZOOLOGY.
10.Fossil Crinoids of the United States.—At the meeting of the American Association, 1849, a paper on the fossil crinoids of Tennessee, by Professor Troost, was read by Professor Agassiz.[90]Thespecies embraced are not less than eighty-eight in number, of which only half a dozen have been described. It is the opinion of Professor Hall that all the silurian formations of New York, previous to the beginning of the geological survey, did not afford more than four or five. Now, about sixty species have been ascertained. Professor Hall mentioned the fact, that all the crinoids of the lower silurian rocks, with the exception of one species, have five pelvic plates, and we never find one with three, or any other number of these plates, before we reach the highest deposits. In Tennessee, the crinoids are so abundant, that Professor Troost states that he had been able to collect some 300 or 400 good specimens of seven or eight different species in a single morning. In relation to the abundance of these fossils in the United States, Professor Agassiz remarked, that it is not, perhaps, sufficiently appreciated of what importance, and of what immense value the study of these fossil crinoids may be for the progress of palæontology. American students should be proud of these materials, by which they will be able to throw so much light upon these almost extinct families by their personal investigations, which will not only render them independent of the palæontologist from abroad for information with regard to the succession of types, and the full illustration of these structures, but really afford correct standards for comparison. It is the more desirable that all these fossils should be made known, as the family of crinoids is so reduced in our days that we can form no idea of the living animals of that group, of their diversity of form, modification of character, and peculiarity of position, from the living type only. He doubted whether the number of crinoid heads of all species found in Europe, now existing in the Museums of Europe, is one-third the number of those which have been found by a single gentleman in Tennessee in one morning. Now, with such materials, consider what precise and what minute investigations could be made. And if these facts could be once fully ascertained and well illustrated, there is no doubt that the series of crinoids, and their succession in former ages, will be established from American standards, and will no longer rest upon the European evidence, which has often been derived from the examination of small fragments of those ancient fossils, found in unconnected basins for the most part, so that their geological succession could be ascertained only with great doubt and difficulty. In conclusion, Professor Agassiz would venture to say, that geologists who have had any opportunity to compare the position of the ancient rocks on this continent of North America with the corresponding deposits of Europe, would agree with him in saying that the geology proper, the stratography of North America, will afford the same precise and well authenticated standards for the appreciation of the order of succession of rocks, as fossils will for the order of succession of living beings.—American Annual of Scientific Discovery,p.282.
11.Discovery of Coral Animals on the Coast of Massachusetts.—Professor Agassiz, while on an expedition in one of the vessels of the coast survey during the past summer, obtained by means of a dredge, from a depth of seventy-two feet, in the Vineyard Sound off Gay Head, several specimens of a coral with its animals. By great care and attention they were preserved alive in glass jars for more than six weeks, and afforded an excellent opportunity for an examination and observation of their structure and habits. These corals belong to the genusAstrangia, and have been named by Professor Agassiz, in honour of Professor Dana, geologist of the exploring expedition, Astrangia Dana.
This species presents two varieties. Some are of a pink or rose colour, others are white. The general form of the animal is a cylinder (as of all Polypi) resting on its base, and expanded on the upper margin; thus expanded it is about two lines in diameter. The number of tentacles is definite, but it is not always the same absolute number. It never exceeds twenty-four; in earlier periods of life there are only twelve, and there is even an epoch when there are only six.
It is, perhaps, a matter of surprise that the coral animal should have been found in this latitude. They teem in the warm latitudes; but there are very few species in the more temperate regions, and but for the opportunity afforded by the coast survey, the existence of these animals could not have been suspected on these shores. For many years, however, dead fragments had been found along the shores; but whether they lived there naturally or not had not been ascertained.—American Annual of Scientific Discovery,p.311.
12.On the Circulation and Digestion of the Lower Animals.—Professor Agassiz states, that the circulation of the invertebrata cannot be compared to that of the vertebrata. Instead of the three conditions of chyme, chyle, and blood, which the circulating fluid of the vertebrata undergoes, the blood of that class of the invertebrata which he had particularly studied, the annelida or worms, is simple coloured chyle. The receptacles of chyle in different parts of the body are true lymphatic hearts, like those found in the vertebrata; this kind of circulation is found in the articulata and mollusks, with few exceptions, and in some of the echinoderms. In the medusæ and polyps, instead of chyle, chyme mixed with water is circulated; this circulation is found in some mollusks and intestinal worms. Professor Agassiz thinks, that the embryological development of the higher animals shews a similar succession in the circulating function. As regards the connection between respiration and circulation in vertebrata, the gills are found between branches of the blood system; in invertebrata, the chyliferous system is acted on by the respiration. The gills of fishes, therefore, cannot be compared to the gills of crustacea, articulata, and mollusks. In fact, no gills are connected withthe chymiferous circulation. Animals having this circulation, have no true respiration. They have only tubes to distribute freshly aërated water to different parts of the body.—Proc. Bost. Nat. Hist. Soc.
13.Distribution of the Testaceous Mollusca of Jamaica.—The great number of species is remarkable. A few miles of coast, without the aid of storms, and without dredging, yielded 450 species. In the small bay of Port Royal, 350 marine species were found. A pint of sand, taken from a surface three yards long, contained 110 species. Probably there are 350 or 400 specimens of land shells, and two or three times as many of marine species. Extensive districts occur, however, which are nearly destitute of land or marine shells. They are accumulated in favourable stations.
The difference in the extent of the distribution of the marine and of the terrestrial species is remarkable. A majority of the marine species are known to occur in the other islands; probably not more than 10 or 15 per cent. of them will be found to be peculiar to Jamaica. But of the land shells, 95 per cent. are peculiar to the island. The limited distribution of the terrestrial species is remarkable. A few are generally distributed, but a large number are limited to districts of a few miles in diameter; and several, although occurring abundantly, could be found only within the space of a few rods. Only seventeen fresh-water species were found. Favourable stations for fresh-water species are rare.
In respect of the number of individuals of mollusca in Jamaica, as compared with more northern latitudes, the rule so obvious in the class of fishes is not applicable to the same extent. Of fishes, the species are much more numerous, but individuals much less so. Of the mollusca, the total number of individuals is about the same as in this latitude, and the number of species represented by a profusion of individuals is about the same. But the number of species not occurring abundantly is much greater, so that the average of individuals to all the species is less than in this latitude. From a comparison of the laws of distribution of the marine and terrestrial species in the Antilles, it follows that the number of the latter must exceed that of the former. With the insular distribution of the terrestrial species may be associated the fact, that the coral reefs are all fringing, for both facts are connected with the geological fact, that these islands are in a process of elevation.—ProfessorAdamsbefore the American Association.—American Annual of Scientific Discovery,p.334.
14.Metamorphoses of the Lepidoptera.—Professor Agassiz said that he had, during the past season, been studying the metamorphoses of the Lepidoptera, and, to his great surprise, he had found that one stage in the transformation of these insects has been overlooked by naturalists. We knew the Lepidoptera in three conditions,—that of the worm, furnished with jaws and jointed, the chrysalis, and the perfect insect with four wings. The change not beforedescribed, which he had noticed, is somewhat concealed under the skin of the caterpillar. The animal at a certain period swells at the thoracic[N31]region, and becomes extremely sensitive to the touch in this part, the skin being, in fact, in a state of inflammation. On cutting open the skin at this place, Professor Agassiz found beneath it a four-winged insect, before it had passed into the chrysalis state. The wings were long enough to extend half the length of the perfect insect. The posterior pair he found to be membraneous bags, somewhat flattened, like the respiratory vesicles of marine worms, with distinct ribs, which are blood-vessels. The anterior pair are also bags, with their upper half stiff and inflexible, like the elytra of coleoptera. The legs are tubular, but not joined, as in the perfect insect. The jaws are changed into two long tubes, which are bent backwards, as are also the antennæ. In the chrysalis, the wings are flattened and soldered together, as are the legs and sucking-tubes, which are bent backwards. The order of development of the different parts and the coleopterous condition at an incomplete stage, show that naturalists have been in error in placing chewing insects, as the coleoptera, above the sucking insects. The order should be reversed. Professor Agassiz said that he had confirmed his observations in many specimens, by examining them just at the moment when the skin begins to split on the back.—American Annual of Scientific Discovery,p.327.
15.On the Zoological Character of Young Mammalia.—At the meeting of the American Association for the Promotion of Science, Professor Agassiz remarked, that zoologists have, in their investigations, constantly neglected one side of their subject, which, when properly considered, will throw a great amount of new light on their investigations. Studying animals, in general, it has been the habit to investigate them in their full grown condition, and scarcely ever to look back for their characters in earlier periods of life. We scarcely ever find, in a book of natural history, a hint as to the difference which exists in the young and old. Perhaps in birds, the colour of the young may be noticed; and it is generally known, that the young resemble the female more than the male; but as to precise investigation of the subject, we are deficient. But if the early stages of life have been neglected, there is one period in the history of animals which has been thoroughly investigated, for the last twenty-five years,—embryology. The changes which take place within the egg itself, and which give rise to the new individual, have been thoroughly examined; but, after the formation of the new being, the changes in its form which it passes through, up to its full grown condition, have been neglected. It had been his object to investigate this subject, because he had been struck with the deficiency there is on this point in our works; and in making this investigation, he had found that the young animals, in almost all classes, differ widely from what they are in their full-grown condition. For instance, a young bat, a youngbird, or a young snake, at a certain period of their growth within the egg, resemble each other so much, that he would defy the most able zoologist of our day to distinguish between a robin and a bat, or between a robin and a snake. There is something of high significance in this fact. There is something common to all these. There is a thought behind these material phenomena, which shews that they are all combined under one rule, and that they only come under different laws of development, to assume, finally, different shapes, according to the object for which they were introduced.
There is a period of life, in which, whatever may be the final form of their organs of locomotion, whatever may be the final difference between the anterior and posterior extremities, vertebrated animals have uniform legs, in the shape of little paddles or fins. This is the case with lizards as well as birds. A robin's wing and a robin's leg, which are so different from a bat's wing and a bat's leg, do not essentially differ when young from the leg and arm of a bat. Wherever we observe combined fingers preserving this condition, we have a decided indication that such animals rank lower in the group to which they belong. This is all-important, as we are enabled at once to group animals which are otherwise allied, in a natural series, as soon as we know whether they have combined or divided fingers. And the degree of division to which the legs rise in their development is a safe guide in our classification. Look, for instance, at the legs of dogs and cats, in which the fingers are completely separated, and so elongated, that the animals walk naturally upon tip-toe, and compare them with others, bears, for instance, which walk upon the whole sole of the foot; and, again, with those of seals or bats, which remain united, and constitute either fins or a wing.
There are other reasons sufficient to convince us that the order of arrangement which he had assigned them, according the development of the fingers, is justified by the state of development of the other organs of the mammalia, and especially of their higher organs and intellectual faculties and instincts. And I will also add, says Professor Agassiz, that mankind are not excluded from this connection, but, in common with other vertebrata, we are all at one stage of existence provided with paddles or fins, which are afterwards developed into legs and arms.—American Annual of Scientific Discovery,p.324.
16.The Manatus or Sea Cow, the Embryonic Type of the Pachydermata?—Professor Agassiz thinks that the Manati have been improperly considered cetaceans: they differ from them in the form of the skull, which is elongated, and in the position of the nostrils, which are in front. On the other hand, the skull resembles that of the elephant in front (particularly when seen from above), in some of the details of the facial bones, which are not like those of the cetacea, in the palatine bones, the arrangement of the teeth, and in the curve of the lower jaw. Professor Agassiz, believedthis to be the true embryonic type of the Pachydermata[N32].—American Annual of Scientific Discovery,p.313.
17.Fossil Elephant and Mastodon from Africa.—M. Gervais communicated to the French Academy, on March 12th, that he had just received from Algiers, a drawing of the molar tooth of a fossil elephant, whose genus is very easily recognised, and which indicates a species more resembling those found in a fossil state in Europe, than the present African elephant. This tooth was found at Cherchell, in the province of Oran. Sicily has hitherto been the southernmost point on the Mediterranean where the fossil elephant has been found.
At the same time, he also mentioned the discovery, near Constantine, of some fossil remains of mastodons. Though fossil remains of this animal have been previously found in all the other portions of the world, these are the first discovered in Africa. The remains found are a tooth and a rib, and, as far as can be judged from a drawing, they belonged to an animal more resembling the mastodon brevirostris, or the arvernensis, than the mastodon angustodens.—American Journal of Scientific Discovery,p.287.
18.Cauterization in the case of Poisonous Bites.—In theComptes Rendusfor January 8th, we find an article byM.Parchappe, containing the result of his observations on the question, whether the spread of poison produced by a bite can be prevented by cauterizing. He was induced to examine into this subject, becauseM.Renard had stated that cauterization was found to have no effect when applied even within five minutes after the bite in the cure of one sort of virus, and within one hour in that of another. These results, he was aware, though derived from experiments upon animals, would weaken the confidence of physicians and patients in the only mode that medicine possesses of preventing the bad effect of a bite from any poisonous animal, where, as is generally the case, some considerable time must elapse before the remedy can be applied.M.Parchappe, accordingly, made several experiments upon dogs, with an extract of nux vomica, all of which go to confirm him in ascribing to cauterization, a power even greater than that commonly allowed it.—“From these experiments it results, that the immediate amputation or destruction in the living portion with which the extract of nux vomica has come in contact, has the power of preventing the bad effects of the poison, even when it has been in contact for some time.”The author is aware, that there is considerable difference between the virus of animals, and the substance used by him, with reference to their direct and remote effects, but thinks that every one must admit that there is a greatanalogybetween them, is of the opinion, that in both cases the poison remains in the bitten part for a considerable time before it is transmitted to the rest of the body, and that cauterizing should be adopted in all cases where a poisonous bite is even suspected.
19.Dental Parasites.—At a meeting of the American Academy, December 1849, a paper was read by Dr H. J. Bowditch, on the animal and vegetable parasites infesting the teeth, with the effects of different agents in causing their removal and destruction. Microscopical examinations had been made of the matter deposited on the teeth and gums of more than forty individuals, selected from all classes of society, in every variety of bodily condition, and in nearly every case animal and vegetable parasites in great numbers had been discovered. Of the animal parasites there were three or four species, and of the vegetable one or two. In fact, the only persons whose mouths were found to be completely free from them cleansed their teeth four times daily, using soap once. One or two of these individuals also passed a thread between the teeth to cleanse them more effectually. In all cases the number of the parasites were greater in proportion to the neglect of cleanliness.