On Preventive Inoculation. 



259 



■disease, almost all its pathogenic power; and it was a question to 

 determine, whether it contained the qualities that were sought for, 

 viz., the power of creating in man a useful degree of resistance to 

 plague. 



The plan has been contested by a number of experimenters who tried 

 a material similarly prepared on different animals and failed to detect 

 in it any immunising properties. 



Among other forms of plague virus which were tested by us, and by 

 other experimenters, a large number were found to be too dangerous' 

 to use ; in other instances the mode of application was inadmissible in 

 the case of men ; in others, again, the effect appeared too transient to 

 be of practical use. 



The Properties of the Plague Prophylactic. 



The immunising effect of the plague prophylactic, as above described, 

 was worked out .on domestic rabbits, and its actual efficiency was 

 verified and confirmed by a number of investigators who experi- 

 mented on the infection with virulent plague of protected and unpro- 

 tected rabbits. 



Comparing the rabbit with other l?Jboratory animals, such as the rat, 

 the guinea pig, the mouse, the monkey, one may consider the rabbit as 

 the one that perhaps required the least amount of protection, as its 

 natural resistance to plague is relatively high. The most altered virus, 

 i.e., such as was rendered the most harmless of all, was found to confer on 

 the rabbit a very considerable degree of immunity, enabling it in a few 

 days to resist ten or fifteen-fold lethal doses of virulent plague microbes. 

 The same treatment applied to animals of a more susceptible nature 

 would, on the contrary, in many instances fail. 



The Questions which were to be solved by Experiments on Human Beings. 



At the end of our laboratory experiments a set of questions stood 

 before us that were to be solved by direct experiment on human 

 beings. Those questions were : — 



1. Would man behave with regard to the prophylactic like the 

 animals upon which its protective power had been worked out ? 



2. If it so happens that the answer is affirmative, what would the 

 dose of the prophylactic, and the method of administering it be ; and 

 would not the dose required be so high, and the reaction to be pro- 

 duced so severe, or the number of inoculations to be repeated so great, 

 as to render the treatment inapplicable to men, or impracticable 1 



3. How many days counting from the date of inoculation would it 

 take to produce in man a useful degree of immunity 1 



4. How long would that immunity last ? 



