RELATIONS OF BACILLI TO THE DISEASE. 321 



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, microscopic- 

 ally resembling another bacillus (the B. coli) which is a 

 normal inhabitant of the animal intestine. This bacillus 

 can be isolated from the Peyer's patches, from the mesenteric 

 glands, the spleen, the liver, the kidneys, and has been 

 found elsewhere in the body. When isolated it is now 

 found by culture reactions to present differences which 

 enable it to be distinguished from the B. coli. The whole 

 series of culture reactions, however, must be investigated 

 before a particular bacillus is identified as the B. typhosus, 

 and no weight must be attached to any observations made 

 on the subject when this has not been done. There are 

 undoubtedly very many cases where organisms have been 

 isolated from various sources resembling closely the B. 

 typhosus on the one hand, and the B. coli on the other, 

 but differing from one or other in some one particular. 

 Cultures, for instance, which otherwise resemble B. coli 

 may not give an indol reaction. The important point here, 

 however, 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. There is no evidence that the 

 B. coli can be transformed into the typhoid bacillus, or the 

 typhoid bacillus into the B. coli, though of course this 

 does not preclude the possibility of the one having been 

 originally derived from the other. All practically are now 

 agreed that two separate bacilli exist, the B. coli and the 

 B. typhosus. 



2. Against the etiological relationship of the latter to the 

 disease several facts may be adduced. First, there is the 

 comparative difficulty of the isolation of the B. typhosus 

 from the stools of typhoid patients. \Ve have pointed out, 

 however, that the latter can be isolated during the first ten 

 days of the disease, and that the extraordinary multiplica- 

 tion of the B. coli, which takes place in any pathological 

 21 



