passing the virus by inoculation from one guineapig to another the rate of its action becomes accelerated. On the other hand, Yersin remarks that, although it is difficult to start a gelatin-peptone cultivation, nevertheless, when obtained, such a cultivation at all events certain parts of such a cultivation will be found to be quite as lethal as virus derived directly from a bubo. He further observes that in such cultures a proportion of the colonies develop more rapidly than others; that if inoculation is made from these more rapidly developed colonies, virulence is found to be diminished; and that if these rapidly growing cultures are frequently repeated, in the long run they cease to be fatal to guineapigs, although they may still prove fatal to white mice.
These and other natural and experimental data indicate a very pronounced tendency to mutability as regards virulence on the part of the plague bacillus: a disposition which, in the future, may very well be turned to important practical account.
It would appear that the gravity of an attack of plague is not affected by the amount of virus introduced. Barber, using an ingenious apparatus, infected guineapigs, each with a single bacillus. The resulting disease was as fatal as that produced by an injection of 500 bacilli.
Experimental plague. Inoculation.— Intentional and unintentional experiments have proved the inoculability of plague in man. Whyte in 1802 communicated the disease to himself, and died of it. At Cairo, in 1835, two condemned criminals were inoculated from the blood of plague patients; they contracted the disease, but recovered. The value of these experiments, as proving inoculability, is somewhat depreciated by the circumstance that they were made in the presence of an epidemic of the disease. Ordinary methods of infection cannot be said, therefore, to have been absolutely excluded. For the same reason the cases of Aoyama and his assistant, who were believed to have contracted the disease from dissection wounds, cannot be held as proving that plague is inoculable in man. The deplor-
