190 
injected and at the same time a dose of antiplague serum inoculated,'* 
but there undoubtedly would be a mortality by such a method, just as in 
rinderpest there is always a certain fatality among cattle when the 
virulent blood and antirinderpestic serum are injected simultaneously, 
and therefore such a method of immunization, though valuable for 
animals, can not be recommended for man. Moreover, it is questionable 
whether any higher immunity in human beings than that which can be 
obtained from the attenuated, harmless culture is usually necessary. 
In publishing for the first time the results of my vaccinations in 
human beings against plague, I wish to sound a note of warning against 
the employment of other strains of living pest bacilli for this purpose. 
Inoculations should not be made in man, unless the investigator can 
guarantee the organism with which he is working to be of sufficient 
attenuation to be no longer dangerous for human beings. Strains of the 
bacillus which invariably no longer kill guinea pigs in doses of two entire 
forty-eight hour agar slant cultures are probably safe in very small 
amounts for human beings. Unless excessive precautions are taken in 
inoculations of living plague bacilli, disastrous results will surely follow. 
It seems probable that by pursuing proper methods for sufficient periods 
of time all strains of pest bacilli perhaps can be attenuated sufficiently 
to be safe for the purposes of human inoculation; although in some 
‘instances it may take several years to bring about such a result. | 
believe that the avirulent pest culture with which these experiments were 
performed is at present hardly more dangerous for inoculation in man 
than is attenuated vaccine taken from human beings sufferig with 
smallpox. 
In concluding this preliminary report I wish to express my thanks to 
Professor Kolle for two of the avirulent pest cultures and again to call 
attention to the fact that it was the careful and extensive work on this 
subject which has come from his laboratory during the past two years 
which convinced me of the value of the living attenuated plague cultures 
in immunization and which caused me to undertake this further study 
of the question in man and animals.'® 
'’ My experiments have convinced me that in pest (as in cholera) unquestionably 
a higher immunity in animals can be obtained with the more virulent organism 
than with the less virulent one. The pest bacillus therefore may differ from the 
typhoid organism in this respect, since Wasserman has shown that this phenom- 
enon does not necessarily result with the latter bacterium. 
“While this article was in press there reached Manila the Centralblatt fiir Bak- 
teriologie [ (1905), 39, 610] containing a report of the experiments of Hueppe and 
Kikuchi on immunization of animals against plague by means of “aggressin” 
obtained according to the method of Bail [Archiv. f. Hyg. (1905), 52, 272). 
The value of immunization with plague “aggressin” prepared after the method 
of Wassermann [Wassermann, and Citron, Deutsche Medizinische Wochenschrift 
(1905), 31, 1101] as compared with that of the living attenuated plague organism 
will be discussed in the more complete report. 
