322 TYPHOID FEVER. 



condition of the intestine, sufficiently explains the failures 

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

 way of accepting the etiological relationship of the B. 

 typhosus lies in the failure to cause the disease in animals. 

 We have noted, however, that there is no evidence that 

 animals are susceptible to the disease. The experiments of 

 Sanarelli ought to have considerable weight in this connec- 

 tion. 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 refractory 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 import- 

 ant, 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 con- 

 valescents, and the peculiar action of such serum in im- 

 mobilising and causing clumping of the bacilli (vide infra] 

 are also of great importance. Especially is this the case 

 when these are taken in conjunction with the fact that 

 the reactions apply only to the typhoid bacillus, and not to 

 other organisms, including the varieties of the B. coli, which 

 resemble it in growth characters, etc. These very important 

 facts may thus be accepted as indirect evidence of the patho- 

 genic relationships of the typhoid bacillus to the disease. 



There is much knowledge yet to be acquired before 

 absolute proof can be obtained, and there is abundant room 

 for discoveries which may modify many of our present 

 views on the bacteriology of the disease ; but according to 

 our present results we must hold that the bacillus typhosus 

 constitutes a distinct species of bacterium, and that it is 

 the cause of typhoid fever. 



The Serum Diagnosis of Typhoid Fever. This method 

 was discovered independently by Widal and Griinbaum in 



