185 
per cent; and with Lustig’s prophylactic, 12 per cent. After reinocula- 
tion (for the purpose of testing the immunity of the rats), 45 per cent of 
those inoculated with the attenuated living organism, 21.9 per cent of 
those which had received the killed agar cultures, 22.2 per cent of those 
injected with Haffkine’s prophylactic, and only 12 per cent of those 
which were given Lustig’s preparation remained alive. 
However, Kolle and Otto’s further experiments on guinea pigs are more 
interesting and conclusive ; for, as these authors have remarked, a prepara- 
tion which is recommended and used for the control of plague in human 
beings should develop a pronounced protective effect on the guinea pig, 
the animal which is the most susceptible to plague. Among fifty-nine 
guinea pigs which they immunized with other attenuated living cultures, 
thirteen died and two were killed for control purposes. The remaining 
forty-four (75 per cent) were tested for their immunity. All of these 
had received but a single injection of the weakened culture; however, 
upon their reinoculation three, four, and eight months after this vaccina- 
tion, twenty-eight (63.6 per cent) remained alive after the injection of 
the virulent organism. Six other guinea pigs received somewhat larger 
doses of a less attenuated culture, and at the same time an injection of 
serum; five survived the vaccination and one died. .Lhe former, upon 
reinoculation with the virulent organism, later all proved to be immune. 
Including the loss during vaccination, there finally remained alive, after 
testing the immunity, 50.8 per cent of the whole series. 
Attempts were made to immunize twenty-six guinea pigs with killed 
agar cultures, amounts as large as from one-half to one entire agar culture 
being injected subcutaneously. During the process of immunization, four 
of the animals died; of the remaining twenty-two, only two (7.7 per cent 
of the whole) proved to be immune on subsequent testing. Hardly more 
favorable results were obtained in the experiments in which killed bouillon 
cultures were employed. Twenty animals were inoculated with Haff- 
kine’s prophylatic; two of these died during immunization and of the 
remaining eighteen, only two (10 per cent) remained alive after rein- 
oculation with the virulent organism. The method of immunization, 
in which Haffkine’s prophylactic was first injected and later followed 
by the introduction of the attenuated living cultures, did not give as 
favorable results as did the living avirulent organism alone. 
In December of the past year (1904) Kolle and Otto™ in further 
detail reported upon the immunization of guinea pigs with the attenuated 
pest bacillus. Among thirty-four of these animals immunized with such 
a culture (Maassen V), of which none died during the process of im- 
munization, twenty-one were reinoculated with a virulent organism one 
to four months after their vaccination, and of this number sixteen (76 
per cent) remained alive, and five died. Nine other guinea pigs were 
inoculated with the avirulent culture, and at the same time with plague 
*% Ztschr. f. Hyg., December (1904), 48, 399. 
