Pasteur announced his discovery ; he was offered a test and accepted. In May, 1881, in the presence of veterinary surgeons, agricul turists, and others, a flock of 50 sheep and 10 cows were brought before him. Into the bodies of 25 sheep and 6 cows he introduced some fluid containing the weakened germ, the remaining 25 sheep and 4 cows were untouched. Three weeks later the most fatal form of the poison was injected into the bodies of all the 50 sheep and 10 cows. Two days later the 25 sheep that had not received the weakened germ were dead, and the 4 cows were very ill, while the 25 sheep and 6 cows which had received it were comfortably browsing. Since that day, up to the end of 1883, more than half a million of animals were vaccinated (so to speak) in France against splenic fever, with a consequent reduction of the death rate from that disease to Ath of what it was among now vaccinated animals.
Briefly, then, splenic fever has been found to be due entirely to the presence in the body of the affected animal of a particular living or ganism, and the result of that knowledge has been to indicate the means for stamping out the disease.
The true nature of another disease, tuber. culosis, has within recent years been revealed by methods of inquiry similar to those just described, pursued by the distinguished Ger man observer, Dr. Koch. It has been stated (p. 372) that tubercle is the chief cause of consumption of the lungs and of the bowels; and of some forms of inflammation of the membranes of the brain (p. 155). In the little nodules of tubercle (p. 375) Koch found a small bacillus (fig. 200). He was able to grow it artificially ; and, by injecting fluid containing his reared germs into animals, he reproduced the disease. In the spit of consumptive patients the germ is found (Plate XXI.). The seeds of the germ are not destroyed by drying, so that when the spit has become dry the seeds may be wafted about in the air, may be drawn into the lungs of a healthy person, and produce the disease. The popular objection, therefore, to sleep with, or be the close companion of, one suffering from con sumption, is not without scientific justification. But the germ of tubercle needs a high tempera ture for its development, and it is not, therefore, likely to thrive in the atmosphere in temperate climates.
After the epidemic of cholera in Egypt in 1883, which spread to France, Italy, and Spain, in vestigations were undertaken to discover whether any special organism could be detected as its cause. French, German, and British commis sioners were appointed for the purpose. Dr. Koch, who was head of the Gorman commission, discovered An organism, a bacillus, or spirillum, shaped like a comma (,)—the "comma bacillus," or "cholera spirillum,"—in the intestines of per sons who had died of cholera, in the discharges from cholera patients, and also in water of which persons had drunk, who had afterwards been seized with cholera. He believed that this was the active agent in the production of the disease. Animals, however, are not susceptible to cholera, and the essential link in the chain of evidence, namely, the production of cholera in animals by the injection into their bodies of the pure cultiva tion of the organism, could not be obtained. In 1885 1)r. Klein, the head of the British commis sion, reported as the result of his investigations his inability to accept Dr. Koch's view. At pre
sent, therefore, the relation of micro-organisms to cholera is not definitely determined.
Malarial fever is due to an organism, though it does not belong to the bacteria (p. 548).
In the blood of persons suffering from relapsing fever spirilla have been found in great numbers, and during the intervals of freedom from fever they disappear from the blood. The fever has been produced in monkeys by injecting into their bodies blood from persons suffering from relapsing fever, and thereafter the spirilla have been found multiplying in the monkey's blood.
In 1884 a bacillus was proved to be the cause of diphtheria.
A micrococcus has been found in erysipelas, and the injection of the reared organism into rabbits produces erysipelas in them.
In the annual reports of the Registrar-General the following diseases are classed as zymotic, that is, as resembling fermentations, and appa rently due to some poison operating in the blood, which poison might consist ©f living organisms such as have been described:— Micrococci have been found in small-pox, scar let fever, diarrhoea of children, and Malta fever. Bacilli have been found in dysentery and typhoid fever. Probably in time research will reveal the connection between all infectious disease and the growth of micro-organisms. How, precisely, the organism operates in the production of the disease it is not easy to determine. It seems probable that the multiplying organism produces some chemical alterations in the blood and tissues of the animal attacked; and it may be that, in the course of its own growth and multiplication, the organism produces some special substance which acts as a poison, and that it is owing to the operation of this poison, or toxin, that the symp. toms of the disease are manifested (sec p. 504). These considerations have some very practical issues. Every infectious or contagious disease appears to be due to some form of micro-organ ism, one particular organism for each particular disease. Each organism produces its own disease and none other ; and the special disease cannot arise unless its germ has gained entrance to the body. They may gain entrance in many ways. They may be present, like putrefactive germs, in the air, in food, in drink. They may be received on one's clothes; they may be harboured under one's thumb-nail; a hostess may dispense thorn with her hospitality ; a friend may impart them by a kiss. But, though the channels by which they spread are inexhaustible, they have one origin and one only, and that is a preceding case of disease. The organisms enter the–body of a person and multiply there. They aro cast off from his body, some by the air which he breathes out, some by his skin, some by the kidneys, some by the way of the intestinal canal. One kind of germ may he particularly abundant in the discharges, may be able to multiply in organic fluids, so that the smallest quantity of such a fluid gaining entrance to food or drink is capable of imparting the disease to those who partake. Another kind of germ, on the other hand, may be drowned, so to speak, in liquid, and may rather be propagated by spores suspended in the air. But that is a mere detail in the life-history of the germ. In all cases, however, it is the introduction of the organism into the body that sets up the disease.