RELATION OF B. TYPHOSUS TO TYPHOID. 343 



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 

 condition of the intestine, sufficiently explains the failures 

 in the later stages. The second and great difficulty in the 

 way of accepting the etiological relationship of the B. 

 typhosus lies in the comparative failure to cause the disease 

 in animals. We have noted, however, that in nature 

 animals do not suffer from typhoid fever. The experiments 

 of Sanarelli ought to have considerable weight in this 

 connection. No other observer has exalted to such a 

 degree the virulence of the typhoid bacillus, which is 

 certainly the rational procedure when dealing with a re- 

 fractory animal. In a way this is unfortunate, for at 

 present Sanarelli's results can be neither confirmed nor 

 denied. We must for the present provisionally accept 

 his statements that both the bacilli of exalted virulence, 

 and what is even more important, the toxines derived from 

 them, give rise to selective pathological changes in Peyer's 

 patches and the mesenteric glands. 



3. The observations of Pfeiffer and others on the pro- 

 tective 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 im- 

 mobilising and causing clumping of the bacilli (vide infra) 

 are also of great importance. These very important facts 

 may thus be accepted as indirect evidence of the patho- 

 genic relationships of the typhoid bacillus to the disease. 



According to our present results we must thus hold 

 that the bacillus typhosus constitutes a distinct species of 

 bacterium, and that there is strong reason for accepting it 

 as the cause of typhoid fever. 



The Serum Diagnosis of Typhoid Fever. This method 

 of diagnosis is based on the fact that living and actively 

 motile typhoid bacilli if placed in the diluted serum of a 

 patient suffering from typhoid fever, within a very short 

 time lose their motility and become aggregated into 

 clumps. The researches which led up to the discovery will 



