RELATIONSHIP TO TYPHOID FEVER 367 



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 Kelationship 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, es[>ecially 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, 

 however, 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 



