This is an infectious disease of animals which may be transmitted to man by inoculation. This occurs, occasionally, from the bite of an insect (fly) which has been feeding upon the carcass of an infected animal ; and also from accidental inoculation while handling hides, wool, etc., taken from the victims of anthrax.
The herbivora are most susceptible to anthrax ; and in certain parts of Europe the annual losses from this disease, among the herds and flocks of the farmers, are very considerable.
The susceptibility of the carnivora to this and other forms of septicaemia is very much less than that of the herbivora. This difference is probably due to natural selection ; for the bodies of herbiv orous animals, dead from anthrax, have doubtless been devoured by the carnivora from the earliest times (anthrax was known to the Greek and Koman physicians) ; and, although inoculation is not liable to occur through the uninjured mucous membrane of the mouth, or of the intestine, it could scarcely fail to occur as a result of wounds inflicted by the teeth and claws of the contestants for the infected prey. An individual difference in susceptibility to the poison, and the survival of the fittest, would in time be very sure to produce a race immunity.
This view is not, however, sustained by the experiments of Prof. Feser upon rats. In these experiments it was found that rats fed on flesh do not contract anthrax, but that the same rats when restricted to a vegetable diet fall victims to the disease after inoculation with anthrax fluids.
The immunity of fowls has been proved by Pasteur to be a question of temperature. According to Chauveau, multiplication of the bacillus in culture-fluids ceases at 43. This is but little above the normal temperature of the fowl. If, however, the temperature is reduced two or three degrees by immersing the lower part of its body in cold water, the fowl becomes susceptible and dies as the result of inoculation with a fluid containing the bacillus.
The anthrax bacillus is said to have been ob served by Pollender in the blood of cattle as early as 1849, and by Davaine in 1850. But the etiological importance of the parasite was first recog nized by the last named observer, and was affirmed in a series of communications to the French Academy, made in 1863 and 1864. The experiments of Davaine established the fact of the presence of rod-shaped bacteria in the blood of animals attacked with charbon, and that a healthy animal into which a small quantity of this blood is injected quickly succumbs to the disease, its blood also being invaded by the parasite.
The view that the infectious properties of an thrax blood depend upon the presence of this parasite was strongly contested, and since Da vaine's first experimental inoculations, a host of investigators have entered the field. The question is admitted by all to be of the greatest importance, and has been most thoroughly investigated by the experimental method, every point made by those in favor of the parasitic-germ theory having been stoutly contested by conservative opponents. The literature of the subject, although so recent, is very voluminous; and the fact that the anthrax bacillus is the essential infectious element in anthrax blood, and that the disease anthrax is due to the multiplication of this parasite in the body of an infected animal, has been established in the face of the most exacting scientific criticism.
Klebs first showed that anthrax blood loses its infectious properties after filtration, while the filtrate is virulent ; but as other solid elements (fibrine and globules) were retained as well as the bacilli, this was not accepted as proof that the latter were the essential infectious particles.
This proof has been furnished by inoculation experiments with pure-cultures of the anthrax bacillus, which have now been made by numerous experimenters in various parts of the world. By successive cultures, in which a small amount of material is used to inoculate a considerable quantity of the culture-fluid, we soon exclude all non living particles, and soluble substances as well, contained in the material introduced as seed into culture No. 1
In such a series, which has been carried as far as the one-hundredth successive culture (Pasteur), the virulence of the last culture-fluid is as great as that of the first ; and, as the culture-fluid itself is innocuous, this virulence can be ascribed only to the living bacilli contained in it, which are the direct descendants of those present in the minute drop of anthrax blood used to inoculate culture No. 1.
Experiments of this kind are conclusive as to the essential etiological role of the anthrax bacil lus, but they do not, of course, explain its modus operandi. Pasteur has shown that the bacillus is aerobic, i.e., that its development depends upon the presence of oxygen, and there can be no doubt that, during its rapid multiplication in the blood of a living animal, it deprives this fluid of its oxygen, and also of other constituents required for its own nutrition. The deprivation of oxygen is shown by the symptoms, dyspnoea, cyanosis, depressed temperature, and finally death, with all the symptoms of asphyxia. It also acts mechan ically, by blocking up the capillaries, and pro ducing emboli and hemorrhagic extravasation in various parts of the body. In addition to this, we have evidence that, as in other forms of septicae mia, a potent chemical poison is produced as a result of vital processes connected with the nutrition of the bacillus. Paul Bert has been able to isolate a poison, diffusible in liquid, which kills in twelve hours. This he accomplished by destroying the bacillus in a fluid containing it by means of com pressed oxygen. Toussaint, also, by injecting filtered anthrax blood, obtained evidence of the presence in it of a poison which, in his experiments, produced only a local inflammation, with out any noticeable constitutional symptoms.
The discovery, which we owe to Koch, that, under favorable conditions, the anthrax bacillus, either in culture-fluids or in the body of a dead animal, develops refrangant, endogenous spores, which have great resisting power against heat and chemical reagents, and may be preserved for years without loss of vitality, has enabled us to account, in a most satisfactory manner, for certain facts which previously seemed to be irreconcilable with a belief in the parasitic-germ theory. Thus Bert treated anthrax blood, which he had received from Alfort, with three times its volume of absolute alcohol, then washed the coagulum in alcohol, and dried it in vacuo. This material, mixed with water and again precipitated by alcohol, proved to be virulent when injected into guinea-pigs. Even after remaining for five months immersed in alco hol, this virus had not lost its potency.
These facts were explained by Pasteur, and, in a subsequent communication, Bert himself explained the mystery. Further experiments had convinced him that virulent fluids containing anthrax rods did not resist either alcohol or compressed oxygen, and that it was only when reproductive spores were present that the flakes of material precipitated by alcohol gave evidence of virulence. Upon microscopical examination these shining spores were detected in the flakes in question, and their continued vitality after the treatment indicated was proved by their germination in a culture fluid.
The anthrax rods are killed by ten minutes' exposure to a temperature of 54 C. (129. 2 Fahr.), by desiccation, and by putrefaction of the fluid containing them, in the absence of oxygen ; but the resting-spores resist prolonged boiling (Pasteur), and are not injuriously affected by desiccation or by putrefaction. Spores are not formed in the rods as they are found in the body of a living animal; but after death, under favorable circum stances, these rods grow into filaments in the interior of which shining oval bodies are developed, which are the spores in question. Thus the car cass of a dead animal may become a storehouse of anthrax seed, which may for many years after its death infect pastures in which the animal was buried. But no development of spores occurs in the absence of oxygen ; and under these circum stances the rods quickly disintegrate and disappear. This is shown by enclosing in a tightly corked bottle blood from an animal recently dead.
Putrefactive decomposition soon takes place, but the blood loses its virulence, and neither rods nor spores can be discovered in it after a few days.
According to Ewart, when cultivated upon a warm stage in albuminous fluids, the anthrax rods become motile within a few hours, and exhibit al ternations of motion and quiescence. This does not correspond with the observations of Koch, and is probably a mistake. Magnin, on page 88 of the present volume, in giving the specific characters of B. anthracis, states that it is always motionless.
If the temperature is maintained at about 33 C.
(91. 4 Fahr.) The rods soon grow into long homo geneous filaments, which in the course of four or five hours may reach a length many times greater (50-100 times) than the original bacilli. These are often twisted and interlaced in the culture fluid. A little later the filaments, which were at first hyaline, are seen to consist of a distinct sheath and a central cylinder of protoplasm, which soon undergoes segmentation, each segment being about the length of the original rods. The spores are formed by a consolidation of the protoplasm of one of these segments into an oval mass, which is subsequently set free by rupture of the cellular envelope, or by its granular disintegration. The oval shining spores after their escape present the appearance of being enclosed in a gelatinous en velope, which according to Koch, is developed into a new rod when germination takes place.
Other observers (Ewart, Cohn) assert that the central protoplasm is developed into a new rod,
