378 TYPHOID FEVER 



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, microscopically resembling other 

 bacilli, especially the b. coli, which is a normal inhabitant of 

 the animal intestine. The bacillus 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 organisms. Here the important 

 point is that 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 of Pfeiffer and others on the protective 

 power against typhoid bacilli shown, on testing in animals, to 

 belong to the serum of typhoid patients and convalescents, and 

 the peculiar action of such serum in immobilising and causing 

 clumping of the bacilli (vide infra), are also of great importance 

 as indicating an etiological relationship between the bacillus and 

 the disease. Additional important evidence is found in the fact 

 that vaccination by means of the dead bacilli (vide infra) has 

 a marked effect in preventing the disease from arising in a 

 population exposed to infection, and also in lowering the 

 mortality when the fever attacks those who have been inoculated. 

 These facts may thus be accepted as indirect but practically 

 conclusive evidence of the pathogenic relationships of the 

 typhoid bacillus to the disease. 



According to our present results, we must thus hold that 

 the b. typhosus constitutes a distinct species of bacterium, and 

 that it is the cause of typhoid fever. Evidence of an important 

 nature confirmatory of this view is, we think, found in the fact 

 that cases have occurred where bacteriologists have accidentally 

 infected themselves by the mouth with pure cultures of the 



