486 Chapter XV 



danger from the protective inoculation is nil or quite trifling. With 

 the exception of the discomfort of which we have spoken and which 

 is transitory, no untoward result has ever been observed. 



To all this must be added the fact that from the point of view 

 of the pathogenesis of typhoid fever, all the probabilities point in 

 favour of the vaccinations. Whilst in Asiatic cholera we have to 

 deal with an intoxication, from the alimentary canal, an intoxication 

 set up by vibrionic products, against which the subcutaneous inocu- 

 lation of micro-organisms can not be efiective, in typhoid fever we 

 have to do with a real infection. The micro-organism, although de- 

 veloped at first in the small intestine, becomes generalised throughout 

 the system. Thanks to improved methods it can always, or almost 

 [509] always, be found in the blood of the patient, and its constant locali- 

 sation in the spleen furnishes a real evidence of this. Under these 

 conditions it is quite natural to suppose that everything which is able 

 to prevent the penetration of the typhoid coccobacillus into the blood 

 and the internal organs ought at the same time to contribute to the 

 protection of the individual. 



We are fully aware that science has not yet said its final word 

 upon this question. We are coming more and more to the conclusion 

 that it is necessary to make two injections instead of one. It is 

 possible that we may have recourse to certain improvements of the 

 method by combining with it the injections of antityphoid serums as 

 a protective measure. The near future will doubtless bring us the 

 solution of these very important questions. 



X. Vaccinations against human plague. Plague, which for so 

 long was looked upon as the greatest scourge of humanity, has until 

 recently remained almost unknown from the scientific point of view. 

 But from the moment that it became possible to apply to its study 

 the immense advances realised by microbiology the thick veil which 

 had hidden its nature fell at a single stroke and science found itself 

 in possession of effective means of fighting against it. Amongst these 

 means one of the most important is protective vaccination. 



When the last pandemic of plague broke out in Bombay and in 

 the East Indies in general, Haff'kine was there engaged in applying 

 his method of vaccination against Asiatic cholera of which we have 

 spoken in the preceding section. Well acquainted with the results 

 of the bacteriological researches made on bubonic plague by 

 Kitasato, and especially by Yersin, he, in 1896, began to study this 



