"I do," continued Dr. Medjora. "It has long been known that certain infectious diseases, such as typhoid fever, are peculiar to man, while the lower animals do not suffer from them; and that, on the other hand, man has a natural immunity from other diseases which are common among the lower animals. Again, some species will resist diseases which become epidemic among others. In addition to an immunity peculiar to a whole race, or species, we have individual differences in susceptibility or resistance. This may be natural, or it may be acquired. For example, the very young are usually more susceptible than adults. But a difference will also be found among adults of a race. The negro is less susceptible to yellow fever than the white man, while, contrarily, small-pox seems to be peculiarly fatal among the dark-skinned races."
"Have the scientists been able to account for these phenomena?"
"They theorize, and many of them are making admirable guesses. They account for race tolerance by the Darwinian theory, of the survival of the fittest. Imagine a susceptible population decimated by a scourge, and the survivors are plainly those who have evidenced a higher power of resistance. Their progeny should show a greater immunity than the original colony, and, after repeated attacks of the same malady, a race tolerance would become a characteristic."
"That is certainly a plausible theory."
"It is probably correct. But acquired immunity, possessed by an individual residing among a people who are susceptible, is the problem of greatest interest. The difference between a susceptible and an immune animal depends upon one fact. In the former, when the disease-breeding germ is introduced, it finds conditions favoring its multiplication, so that it makes increasing invasions into the tissues. The immune animal resists such multiplication, and possesses inherent powers of resistance which finally exterminates the invader. But how can this immunity be acquired by a given individual?"
"Upon the solution of that question, I would say depends the future extermination of disease," said the Judge.
"You are right," assented the Doctor. "Ogata and Jashuhara have recorded some interesting experiments. They cultivated the bacillus of anthrax in the blood of an animal immune to that disease, and when they injected these cultures into a susceptible animal, they found that only a mild attack of the disease ensued, and that subsequently the animal was immune to further inoculation."
"Why, if that is so, it would seem that we have only to use the blood of immune animals, as an injection, to insure a person against a disease!"
"Behring and Kitasato experimenting in that direction, found that the blood of immune animals, injected into susceptible individuals, after twenty-four hours rendered them immune, but this would not follow with all diseases. In many maladies common to man, a single attack, from which the person recovers, renders him safe from future epidemics. The most commonly known example of this is the discovery by Jenner, who gave the world that safeguard against small-pox, known as vaccination. But the most important discovery in this direction yet made is one which is not fully appreciated even by the discoverer himself. Chauveau, in 1880, ascertained that, if he protected ewes by inoculating them with an attenuated virus, their lambs, when born, would show an acquired immunity."
"This is incredible!"