183 
the commission abandoned the idea of employing the living organism 
for the purpose of obtaining immunity against the disease. 
Albrecht and Gohn'® (the Austrian Plague Commission) performed 
experiments with attenuated plague cultures on eight guinea pigs and 
twenty-seven rats. Of the guinea pigs inoculated, either subcutaneously 
or intraperitoneally, with the living organism of reduced virulence, and 
later repeatedly reinoculated with increasing doses of a virulent culture, 
five finally died and three remained alive. The immunity was found still 
to be present in some of the animals seven months after the vaccination. 
It is not altogether clear why repeated and increasing amounts of the 
more virulent organism were injected in testing the immunity of the 
guinea pigs, unless the authors felt uncertain of the exact virulence of 
the culture which they used or of the method they employed. 
Kolle has recently criticised some of this experimental work more in 
detail, referring particularly to the fact that the animals were, at least in 
some cases, reinoculated with the virulent culture at too short a time 
after the vaccination, for the results of the experiments to be conclusive, 
since in some instances they might have been suffering from chronic pest 
at the time of the reinoculation. Besides this, the quantity of the bacteria 
injected in testing the immunity of some of the animals was very large. 
‘Twenty-one of the twenty-seven rats which Albrecht and Gohn vaccinated 
remained alive after reinoculation with the virulent organism. Only 
one experiment was performed upon a monkey; in this instance the 
animal was apparently immunized successfully, but it finally died of 
tuberculosis. Albrecht and Gohn conclude that immunity can be obtained 
in animals by employing the living pest bacillus, but that this process 
must be carried on in a careful manner in order obtain a fair degree of 
protection. From their experiments they were unable to decide whether 
the immunity caused by the injection of the killed pest bacillus was fully 
as great as that which resulted from the inoculation of the living 
organisms. 
Yersin and Carré! also performed experiments upon the immuniza- 
tion of rats with attenuated strains of the plague bacillus. They finally 
obtained a culture of such diminished virulence that only one-fifth of the 
animals vaccinated with this organism succumbed to the effects of the 
injection. <A series of twenty-five rats was inoculated with this culture. 
Three of these died from the effects of the vaccination and about three 
weeks later the remaining twenty-two animals were inoculated with the 
virulent pest organism, after which only one succumbed. A second series 
of twenty rats was inoculated with the same bacillus. Ten of these, 
which survived the vaccination, were later inoculated with the virulent 
® Denkschrift d. math.-naturw. Klasse d. Kaiserl. Akad. Wien (1898 and 1900), 
66, 807. 
™ Congrés International de Médecine, Section de Médecine et Chirugie Militaires. 
Sous-section Coloniale, Paris (1904), 54. 
