RELATIONSHIP OF B. TYPHOSUS TO TYPHOID 369 



(see chapter on Immunity). Pfeiffer, for example, found on 

 adding serum from typhoid convalescents to typhoid bacilli 

 killed by heat, and injecting the mixture into guinea-pigs, that 

 death took place as in control animals which had received these 

 toxic agents alone. Pfeiffer also found that by using the serum 

 of immunised goats, he could, to a certain extent, protect other 

 animals against the subsequent injection of virulent living 

 typhoid bacilli. On trying to use the agent in a curative way, 

 i.e., injecting it only after the bacilli had begun to produce their 

 effects, he got little or no result. , 



General View of the Relationship of the B. typhosus to 

 Typhoid Fever. — 1. We see in typhoid fever a disease having 

 its centre in and about the intestine, and acting secondarily on 

 many other parts of the body. In the parts most affected there 

 is always a bacillus present, which can be isolated from the 

 characteristic lesions of the disease and from other parts of the 

 body as described, and further, it is found by culture and serum 

 reactions to differ from other organism. A bacillus giving all 

 the reactions of the typhoid bacillus has never been isolated 

 except from cases of typhoid fever, or under circumstances that 

 make it possible for the bacillus in question to have been derived 

 from a case of typhoid fever. 



2. A difficulty in the way of accepting the etiological relation- 

 ship of the b. typhosus lies in the comparative failure of 

 attempts to cause the disease in animals. We have noted, how- 

 ever, that in nature animals do not suffer from typhoid fever. 



3. The observations on the protective power against typhoid 

 bacilli shown to belong to the serum of typhoid patients and 

 convalescents, and the action of such serum in agglutinating the 

 bacilli (vide infra), indicate an etiological relationship between 

 the bacillus and the disease. Additional evidence is found in 

 the fact that vaccination with the dead bacilli (vide infra) has 

 a marked effect in preventing the disease from arising in those 

 exposed to infection, and also in lowering the mortality when 

 the fever attacks inoculated persons. 



These facts constitute indirect but practically conclusive evi- 

 dence of the causal relationship of the typhoid bacillus to the 

 disease. Confirmation of this view is found in the fact that 

 cases have occurred where bacteriologists have accidentally in- 

 fected themselves by the mouth with pure cultures of the 

 typhoid bacillus, and after the usual incubation period have 

 developed typhoid fever. Several cases of this kind have been 

 brought to our notice, and are not, we think, vitiated by the fact 

 that other similar instances have occurred without the subsequent 



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