334 TYPHOID FEVER 



General View of the Relationship of the B. typhosus to 

 Typhoid Fever. 1. We have 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. This 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 popula- 

 tion 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 

 typhoid bacillus, and after the usual incubation period has 

 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 

 development of illness. These latter would be accounted for by 



