We have already seen, in the preceding chapter, that the microbes and the cells of various organisms are capable of secreting definite products of a toxic nature to which the names "ptomaines" and "leucomaines" have been given. Researches, which were begun scarcely twenty years ago, have shown that, besides these crystallizable and definite products, we meet with basic non-crystallizable substances of unknown composition, possessing special toxic properties, sometimes even of extreme violence. These substances have been named "toxins."
At first this generic name was extended toward indefinite basic organic products that could be isolated from tissues and tumors both normal and abnormal; later on, however, the name was applied to toxic substances, equally indefinite, isolated from the culture media of microbes and the active constituent of various venoms.
It is only since 1885, when Charrin called attention to them, that investigations began to bemade regarding them. In 1888 Roux and Yersin,21in their beautiful researches on diphtheria, pointed out the diastatic nature of the properties of the active albuminoid matter existing in the cultures of the specific bacilli of this disease. From that period, these products began to take a more and more prominent place, from year to year, in the study of pathological affections, and, by developing the knowledge of immunity, they have opened a new path to the investigations of therapeutic technic.
It is due to the knowledge of these principles that we have learned that the infectious microbes, far from acting as they were believed to do only a few years ago, and which Pasteur strongly maintained to be by vital parasitism—such as would be the case with the carbonizing bacteria which, according to Pasteur, act by diverting the oxygen, or causing capillary embolisms—owe their pathogenic action to the toxic substances which are the products of their secretion, and which spread throughout the organism, even though the microbe frequently is localized in a very circumscribed spot, as in tetanus and in diphtheria.
The idea of intoxication by these products has now replaced the idea of the direct action of themicrobe on the elements or the liquids of the organism.
The occurrence that takes place in diphtheria and tetanus is one of the best examples to cite in support of this view.
Here, in fact, the pathogenic microbe is found only in a very limited area in the organism attacked—the false membrane, in the case of diphtheria, or frequently only a slight wound in the case of tetanus, and the microbe becomes localized there only. Now, in both cases, there are general phenomena of toxic effects. There must hence be a diffusion of toxic substances which, distributed by the blood, affect the different systems and exert a toxic action on the entire organism.
It must be observed thatthe toxins act as toxic agents only when in a condition to be introduced into the circulation subcutaneously. The cause of this innocuousness of the toxins when given per os has frequently been studied. It appears to be quite probable that the cause of the attenuation of the morbid properties is due to the intervention of the digestive microbes. Such is the opinion of Levaditi and Charrin22; it is also the conclusion that is to be drawn from the experiments of Mme. Metchnikoff and of Calmette23on the modifications undergone by a vegetable toxalbumin, abrin, and by serpent venoms, when these toxalbumins are inoculated with the bacillus subtilis chromogenus. Moreover, Charrin and Lefèvre,24on the one hand, and Nencki, Sieber and Somanowsky,25and Carrière,26on the other hand, have discovered that the digestive ferments, particularly trypsin, destroy, even though but little, the toxins secreted by the Loeffler and Nicolaier bacilli. This is practically contrary to the opinion of Behring and of Rauson,27according to which the innocuousness of the microbial poisons when administered per os is due exclusively to the lack of absorption.
Nature of the Toxins.—The molecules of the toxins are very nearly like those of the diastases. Like these, the toxins appear to have a very complex, and very unstable, internal structure. Their mode of action frequently depends, as in the case of the diastases, upon the medium in which they occur. Again, like the diastases, they are generally destroyed by the action of sufficiently prolonged heat, but less easily, for there are certain toxins that resist a temperature of 100° C. for an indefinite period. They are, like the diastatic albuminoids,insoluble in strong alcohol, and are precipitated from their solutions on the addition of this reagent. They easily adhere to precipitates that form in liquids in which they occur in solution, and possess the remarkable property of diastases in that imponderable masses produce considerable results.28
Although closely allied to certain alkaloidal bases, the toxins are sharply distinguished by the remarkable fact that their action is never immediate, but is always preceded by a period of incubation, which may be quite long.
Like the alkaloidal bases, they appear to result from the hydrolyzing breaking down of albuminoids and nucleo-albumins, and they appear to be intermediary, from a chemical point of view, between these bodies, the general characters of which they retain, and the alkaloids proper, or ptomaines, to which we have called attention, and the principal chemical and physiological properties of which they possess.
No absolutely precise knowledge is had regarding the chemical nature and constitution of these remarkable substances. A number of analyses of these substances have been published which, in general, permit no definite conclusion to be drawn.29I have, however, elaborated several speculative ideas regarding this subject.30
We must here call particular attention to the ideas of Ehrlich regarding the constitution of the toxins. According to this scientist, their molecules contain two functional groups; the one, to which he has given the name "haptophore," is that which enables the toxin to attach itself to any cellular element whatever, and which it then renders non-toxic by means of the other, or "toxophore," group. We will particularize farther on regarding this very important conception.
Origin of the Toxins.—These toxic bodies result either as the products of the secretion of microbial life, or as the result of the normal functionation of cellular life in the higher vegetable or animal organisms.
They are the direct products of life, and do not result, as was formerly believed, from a more or less profound modification of the more or less complex albuminoids that serve as a food for the various species of microbes, or for the cellular elements.
The vegetable toxins are less numerous thanthe animal toxins. They are met with, nevertheless, in almost all mushrooms which are reputed or known to be toxic; the seed of the castor plant contains a very toxic vegetable albuminoid, as is likewise the case with Abrus precatorius (jequirity-bean), and certain others.
The true physiological toxins occupy a very important place in the realization of the conditions that govern health, sickness, and death.
We will see later on that they are met with in quite large number in the bladder, whence they are voided in the urine. Their number varies considerably, according to diverse influences (waking, slumber, eating, fasting, fatigue, oxygen, brainwork, health, disease, etc.). It is necessary here to observe that the renal system serves for the purification of the entire organism, and that in the case of normal life we will find in the renal system a large portion of the products of the cellular secretion of the organism, and among the number there are found, as we know, a certain number of alkaloidal bases. We will take up later the subject of urinary toxicity.
Autointoxications.—The toxins are also encountered, and often in some number, in the muscular tissues and in the blood, particularly in those of batrachians, mureids, and saurians. In the organism these toxins, developed by the activity of the various cells, may cause autointoxicationwhenever, for one cause or another, their normal elimination ceases. "Although there are an infinity of diseases," remarked Prof. Bouchard, "there are but a few ways of becoming ill." Of these ways that of autointoxication is the most frequent. "What else is it, then," says Prof. Charrin, "in the last analysis, but to die from affections of the kidney, the liver, the heart, the lung, etc., if it be not to succumb because of the lack of oxygen, the accumulation of carbonic acid, the influence of the numerous urinary poisons, the action of acids, of salts, of biliary pigments, or the effect of noxious principles, which the hepatic cell must normally destroy or at least attenuate."
These autointoxications, always due to poor elimination of toxic principles, toxins formed in very great number in the organism, and which the normal modes of evacuation or destruction do not eliminate, are always found to be the cause of all diseases, even those that are manifested by attacks of the cerebro-spinal axis, and that exhibit variously mania, insanity, symptoms of hyperexcitability, etc.
These autointoxications are controlled by the nervous system, and the latter alone is the cause of a larger number of maladies than is generally believed; in fact, if the mechanism of nutrition be reduced to its most simple elements, it will be seen to consist of the penetration of the foods, ofthe plasmatic principles, to the cells; of their transformation within the interior of the cells, and finally the rejection of all the matter that could not be utilized. It is the nervous system that commands or dominates this mechanism, that controls the taking-up of assimilable elements and the elimination of toxic principles, the fruit of assimilation or disassimilation, and in such a manner, in fact, that this same nervous system can, at its will, cause starvation, or intoxicate.
The marvelous cures obtained by magnetic methods are due to no other causes than favorable changes in the nervous system.
General Mode of Action.—The toxins, of whatever kind, always behave like diastases, in the sense that their definite action appears to be absolutely independent of their mass, and that imponderable quantities suffice to cause serious morbid affections and profound modifications in nutrition.
Koch has shown that tuberculin is capable of affecting 60 trillion times its weight of the living human being. According to Vaillard one milligramme of tetanus toxin will kill a horse weighing 600 kilos. These two examples show what an enormous power the toxins possess.
My views regarding the manner in which diastases act I have developed at length in my workNature des Diastases. The close analogy between these substances and the toxins, an analogy uponwhich, moreover, I have dwelt at some length, permits me to refer the reader who is desirous of fuller details to the small work just mentioned.
The mode of action of diastases resembles singularly closely that of the catalytic substances, and we will admit, for the moment, that they act by intermediary combination, resulting in their rapid decomposition.
We owe to Ehrlich31a new conception relative to the nature and mode of action of the diastases, and which to-day plays an important rôle in all our conceptions regarding immunity.32
According to this scientist, the complex molecule of albuminoid substances is constituted by a fixed central nucleus, and by a number of lateral chains or receptors, fixed to this nucleus, which possess diverse accessory functions, and which serve, particularly, for the nutrition of the cells. These receptors have a great affinity for the various substances necessary for the support of the living elements, and they seize upon the alimentary substances, in normal life, just as a leaf of theDionæaseizes a fly which serves as its food.
In these special conditions the receptors mayattach themselves to the complex molecules of albuminoid substances, such as the different toxins.
Ehrlich supposes, as we have already seen, that a toxin contains two special groups—atoxophoregroup, which poisons, and ahaptophoregroup, which combines with the receptor. According to this theory, the toxophore group of a toxin can act on an organismonlywhen the haptophore group of the toxin encounters a suitable attachment or receptor.
The receptors attached to the living protoplasmic molecule attract the toxin, just as a lightning-rod attracts the lightning.
It is hence clearly proved that the toxigenic poisons exert their noxious action on the cellular elements of sensitive organisms, by entering into combination with these.
Experience has shown that they attach themselves, in a most rigorously elective manner, to the tissues, and rapidly disappear from the general circulation. Numerous facts, clearly established, attest the reality of this fixation or attachment.
It is thus that von Behring and Wernicke33sought to ascertain the quantity of antitoxin (we will see farther on that this name is given to those substances which neutralize the activity of toxinsunder certain conditions) which, introduced a certain time after the introduction of the poison, will save the life of the animal. They have experimented with diphtheria toxin, which we will study later, and they have demonstrated that, if the antitoxic serum be introduced immediately after the toxin, a dose of antitoxin twice as large as that of the toxin suffices to effect a cure.
Eight hours after the administration of the toxin the dose must be trebled, while after thirty-six hours it is necessary to have recourse to a quantity of antitoxin eight times as great. These experiments show that the curative action of the antitoxin is so much the less the longer the period of time that has elapsed between the introduction of the toxin and the antitoxin. This is because the toxin has become so intimately attached to the tissues that the antitoxin introduced has not the power to destroy the combination. These facts have been confirmed by Donitz34and by the classic experiments of Decroly and Rousse.35
This is not, however, the case with cold-blooded animals, which, generally, are not affected by injections of poisonous toxins. Thus Metchnikoff36andhis pupils have been able to show that the toxins introduced into certain cold-blooded animals (Oryetes nasicorius) may remain for several months without alteration in their circulation.
If we consider the facts of the theory of Ehrlich's lateral chains, which we have mentioned, we are led to well-defined conclusions regarding the mode of action of the toxins. In fact, since these toxins exhibit a pronounced chemical affinity for the tissues, and while, on the other hand, they can attach themselves only because of the presence of certain functional groups of the protoplasmic molecules, this union can take place only in certain specific centers. This has been fully confirmed by experimentsin vitro.
It is known, since the researches of Ehrlich,37Wassermann and Takaki,38Marie,39Metchnikoff,40and a host of other scientists, that this fixation is due to a clearly elective property. It is for this reason that the tetanus toxin fixes itself only upon the nervous tissue, and that in this action all passes as if the nervous tissue had been provided withfunctional groups possessing an elective affinity for the tetanic poison.
Means of Defense Possessed by the Organism against the Action of Toxins.—We have already seen that the renal organs serve for the elimination of the toxins normally produced in the organism by the simple play of its cellular mechanism. Experience has shown that the toxins introduced from without into the circulation are generally finally eliminated, even though in the meantime the modifications they have imprinted on the economy may be transmitted hereditarily; and that their influence on the general nutrition and the normal functionation of the entire organism persists even after their elimination.
Much has been said regarding the elimination of these toxins by the urine, but the experiments made by Métin, at the Institut Pasteur, have shown the inaccuracy of this assumption, and it has been necessary to seek another.
It has been remarked that oxidation destroys the toxinsin vitro, and it has been thought that a process resembling disinfection may well take place within the tissues of the animal economy, but no decision has been arrived at regarding the possible mechanism of this action, which some attribute to the action of the oxidizing ferments of the organism, or to the action of certain special cells.
According to Poehl, there is developed as destroyer a substance possessing energetic oxidizing properties, which he has isolated and namedspermine, and which is found in most of the organic fluids and particularly in the leucocytes, the special rôle of which we will presently study.
There develops still another cause of elimination, or, to be more exact, of the neutralization of the toxic principles in defense of the organism against the toxins, and that is the formation ofantitoxins.
It is well known that the termvirushas been reserved to designate physiological liquids which were characterized, when first they were known, by their property of transmitting to an organism certain functional affections, but the true character of which is to expend their toxicity upon the microbes which occur and are reproduced in the organism, or upon the organized plastidulary granulations, as in the case of the rabic virus, the special microbe of which has not as yet been isolated.
Pasteur, when studying rabies, found that the brain and spinal marrow of rabid animals contained the pure rabic virus in considerable quantity, and that every particle of the marrow was capable of imparting rabies to a perfectly healthy dog. After having ascertained this fact, he found that he couldattenuate the action of the virus, either by passing the virus through certain animal organisms, suchas the monkey or rabbit, by gently heating, or even by allowing it to oxidize and partially dry in the air, or else by submitting it to the action of antiseptics or alternating electric currents of very high tension.
Experiments have shown that a deadly virus, attenuated by one of the means mentioned, may be injected, without danger of death, into the living animal; and what is still better, the animal thus treated acquires the power of resisting large doses of the virus, less and less attenuated, and that it is possible to reach a point where the animal economy may become habituated to very large doses of a highly virulent virus without the organism experiencing any visible illness—that is, the organism has beenvaccinatedwith regard to the particular virus.
Experiments have shown that this property is not peculiar to microbial virus alone, but that it is common to the venoms the toxicity of which is essentially due to some toxins, with the exception of those agents noted.
The attenuatedviruses act, as vaccins, through their soluble constituents, which, either directly, by modifying the nutrition of certain cells, or indirectly, by inducing reactions of the nervous centers which preside over this nutrition, profoundly change the conditions of life and give rise to the pathological condition—the vaccined state.
Experiments by Behring and Kitasato41have shown that the tumors of a vaccinated animal, freed from all organized matter visible under the microscope by filtration through porcelain, contains principles capable of directly or indirectly protecting other animals from the disease caused by the corresponding virus. Meanwhile, experiments have shown that the vaccinating matters are totally eliminated; nevertheless, after their elimination, the immunity acquired remains with the animal, which then continues to be protected against the corresponding virus.
Interest in this subject has incited numerous researches with a regard to bringing to light the mechanism of this immunization; and this will form the subject of another volume of this collection. We may state here, however, that there have been recognized two concurrent causes of this preservative action; the one, calledphagocytosis, results from the fact that the microbe introduced into the vaccined organism becomes incapable of producing its usual toxins, while on the other hand the immunization renders the organism capable of secreting substances possessing an activity contrary to that of the virus, in fact true counter-poisons, comprised under the general nameantitoxins.
Phagocytosis.—We have seen that an organism subjected to a toxic invasion tends to protect itself by proper means of defense; and one of those is the direct putting into activity of the living cellular elements themselves, and in particular, the leucocytes, or white corpuscles, found in more or less number, according to pathological conditions, in the blood and lymphatic fluids.42
Metchnikoff has shown that the moment a foreign element, particularly a microbe, enters the organism, these leucocytes come flocking from all parts of the body, collect around the bacterial element, penetrate it, and begin to digest it. These elements have received the namephagocytes. The namechemotaxishas been given to the property by virtue of which they approach (positive chemotaxis) or move away from (negative chemotaxis) certain substances which affect them powerfully.
Experiments have shown that the leucocytes are attracted by the products secreted by pathogenic microbes, or saprophytes. Attracted by the latter, the white corpuscles surround, envelop, and finally digest them; and when it happens that all the pathogenic microbes within an organismare absorbed, the organism survives, while in the contrary case it succumbs.
Attention must be called to this attack by the white corpuscles within the limits where they are normally confined. It is a pathologic diapedesis—a leucocytosis provoked by the irritation of the tissues—and caused either by the presence alone of foreign elements, or by the soluble products secreted by them.
When, for any reason whatever, this phagocytic action is impeded, the resistance of the organism to pathogenic infection ceases to be effective, and the organism may therefore be invaded by the microbe. Numerous causes may contribute to impede this action.
The Antitoxins.
We have seen that the second means of defense possessed by the organism resides in the action of special products, true defensive secretions, possessing an activity contrary to that of the toxins, and which are secreted by the cells of the organism under the influence of the vaccins.
This is a property common to every organism, and which is observed even in non-vaccinated subjects, although in this case the secretion forms with great difficulty and in small quantity.
When an organism subjected to the toxic action of a bacterial infection does not succumb to theintoxication, it emerges from the test gifted with a new property, which may be augmented by habituation, and which borders on immunity.
At first we were content to vaccinate small animals in the laboratory, but in proportion as the discoveries in this domain extended, and there developed a need for large quantities of antitoxins, recourse was had to the larger animals, particularly horses and cattle. From the moment that large quantities of blood and antitoxic serum were at command, search was made for a means of isolating the antitoxin and determining its properties.
Experiments so far made have shown that the antitoxins are substances of an albuminoid nature, of unknown composition, and which are very closely united to the albuminoid substances of the serum. It must be observed, however, that Behring and Knorr oppose the assertion regarding the albuminoid nature of tetanic antitoxin, but their reasons for this do not appear to be well founded.
In general, these antitoxins are precipitable with the globulins, and possess quite considerable powers of resistance towards physical and chemical agents. Thus they are destroyed only at a temperature above 60-65° C. Kept in the dry state, in the residue of evaporated serum, and away from the light and all oxidizing action, it is possible to preserve their activity for a very long time.
They are essentially humoral substances; theyare found in the blood of vaccinated animals, from which may be obtained antitoxic serums with a specific but transient immunity; and they are also found in the plasmas of the lymph and exudates, in aqueous tumors, and in the milk. They are seldom found in the cells.
Mode of Action.—Frequent attention has been paid to the mode of action of the antitoxins upon the toxins, a phenomenon of great importance in relation to the phenomenon of immunity acquired against the toxins. At the beginning of our knowledge on this subject, the idea of a destruction of the toxin immediately suggested itself, and was advanced by von Behring.43According to this scientist the antibody inhibits the morbigenic action of the toxin by neutralizing the toxin, combining with the latter to form a compound of a chemical nature which is devoid of toxicity and without action on the organism. According to this theory, the influence of the antitoxin on the toxin is direct, and does not require the intervention of the living cellular protoplasm. Such was also the belief of Prof. Ehrlich.44
Buchner, a little later, believed that the antitoxin, instead of acting directly on the toxin, exercised a direct influence on the living elementsof the organism, preserving them from intoxication.45
Such was also the opinion of Roux46; and Calmette demonstrated that a mixture of venom and of a non-toxic antivenom recovered its toxicity on being heated to 68° C, whereby the antivenom was destroyed (Calmette:Le Venin des Serpents, Paris, 1897, p. 58); and Wassermann arrived at the same result.47
The array of proofs offered by these scientists, which we cannot here enlarge upon without uselessly extending our subject, would tend to make one believe, at first glance, that the antitoxin does not act directly on the toxin, but at the present time Buchner's theory appears untenable. Numerous researches have proved conclusively that the toxin and the antitoxin have a specific affinity for each other, by virtue of which these principles combine to form a substance free from all toxicity, but unstable, and which may be decomposed by heat or certain other factors.48
Some recent experiments by J. Martin and Cherry (Proceedings of the Royal Society, 1898,LXIII, p. 423) have clearly brought out this fact. These authors made mixtures of serpent venom with itsantivenom, which they filtered through a layer of gelatin, under the supposition that, if the venom and its antivenom were not chemically combined, the former alone would be able to pass through into the filtrate, because its molecules are so much smaller. Martin and Cherry allowed the venom and its antivenom to remain in contact for varying periods before filtering. As the result of a series of experiments carried out with this idea, they have demonstrated that the filtrate obtained after allowing a few minutes' contact between the two substances, was decidedly toxic, while that obtained after a contact of half an hour was absolutely non-toxic. From this the authors conclude that the antitoxin enters into chemical union with the venom, but that the combination does not take place immediately, and requires a certain length of time for its accomplishment.
Ehrlich and Knorr have demonstrated that the neutralization is less rapid in dilute solutions than in concentrated ones.
Prof. Svante Arrhenius has completed our knowledge regarding the mode of combination between the toxins and the antitoxins, by demonstrating the occurrence of limited reactions analogous to the etherification of an alcohol by an acid, and in such a manner that there always exists, in a mixture of these two substances, a certain quantity of free toxin and antitoxin. This is an importantmodification of the general ideas held in this respect.49
It appears necessary to bring here more clearly in evidence the fact thatthe antitoxin inhibits the noxious action of the toxin, even outside the living organism, by uniting with it to form a compound in identically the same manner as when a strong base and a strong acid are brought together. As we have seen, all the conditions of environment that favor or retard the formation of salts, in a like sense influence the neutralization of the toxin by its antitoxin.
Formation of Antitoxins.—Ehrlich's theory of side chains, to which reference has already been made, furnishes us with an explanation of the formation of the antitoxins in tumors. Let us suppose that, in the organism, a cell had come into contact only with certain toxic molecules incapable of compromising its life, and that the only result was the immobilization of the receptors which are united with the haptophore groups of the opposing toxins. It is known that, by virtue of a property inherent in all living organisms, during the phenomena of reparation, there is generally an overproduction of the neoformedparts. In the case we here speak of, as the receptors fill an important function in the nutrition of the opposing cellular elements, once they become united with the toxic haptophores, they become incapable of filling their normal function of nutrition. Under these conditions the cells develop so large a quantity of receptors that, filling the cells, and not finding any more room, they spread into the blood and other liquids of the organism.
Under these conditions, every new injection of toxin into the organism is absorbed into the blood where it meets with the free receptors which possess great avidity for the haptophore group of its molecule, and the two groups immediately unite, before the haptophore group of the toxin has been able to attack and intoxicate a cellular element.
We thus see that the receptors which, when in a free state in tumors, play the rôle of antitoxics or antitoxins, become, within the cellular elements themselves, the vehicle of intoxications. Figuratively speaking, so long as these fixators are attached to the molecule of the living protoplasm they attract the toxin.
According to this ingenious conception, the formation of antitoxins is hence absolutely independent of the action of the toxophore elements on the cellular elements, and it suffices that these possess receptors or side chains capable of uniting with the haptophore groups of the toxin. This explainswhy it has been possible to produce antitoxins from toxins which have lost some of their toxic properties, but which have preserved their property of uniting with antitoxic substances. Ehrlich gives the nametoxoidsto those modified toxins that have lost their toxophore groups, while the haptophore group, the producer of the immunizing substance, is still preserved intact.
According to Metchnikoff's theory, which is very similar, it seems quite possible that the phagocytes, thanks to the facility with which they absorb poisons, occupy an important place as producers of antitoxins. It has not been possible so far to verify this theory in our at present imperfect knowledge regarding this subject. The domain of immunity has, however, made brilliant conquests during these last few years, so that we should not despair of arriving at a definite solution before long.
In the vaccinated animal the antitoxin is reproduced, and it is possible to obtain several times, from the vaccinated animals, successive portions of antitoxic serum.50The protective power of these antitoxins is absolutely marvelous. An animal accustomed gradually to the tetanic virus yields a serum containing an antitoxin a thousand times more active than the virus.
According to Vaillard, a quintillionth of a cubic centimeter of this antitetanic serum suffices to preserve one gramme of living mouse from the effects of a dose of tetanic serum that would otherwise be surely fatal.
In the animal, the antitoxins are eliminated mostly by the fluids of the body, and particularly by the urine. Ehrlich has demonstrated that they also pass into the milk, and this fact is confirmed by a large number of observers. It explains the immunity acquired by nurslings, and which is transmitted by the milk.
Serotherapy.—The search for antitoxins and their rôle in the etiology of infectious diseases are fundamental points in actual therapy. It has been demonstrated that the serums of certain vaccinated animals enjoy very extended antitoxic therapeutic properties; for instance, the serum of vaccinated rabbits is an antivenom towards erysipelas; and the sterilized cultures of the pneumococcus or of the Bacillus pyocyaneus prevents infection of carbuncle (anthrax).
The antivenomous serum of the ass immunized by injections of increasing doses of the venom of the terrible naja is a perfect prophylactic and curative, not only as regards the venom of this serpent, but also against that of the crotalus, trigonocephalus, and viper.
We shall take up the study of serotherapeutics in another volume of this collection.