PATHOLOGICAL CHANGES^ 329 



this test will be discussed later (see Immunity). Here we may 

 say that a negative result obtained with a suspected b. 

 typhosus culture is of greater value than a positive result 

 obtained with a suspected b. coli culture. The test is to be 

 taken in conjunction with the other means of differentiating the 

 two organisms (cf. p. 340). 



It will thus be seen that the diagnosis between the b. 

 typhosus and the b. coli is a matter of no small difficulty. 

 There is no evidence that the one organism ever passes into the 

 other. Great difficulties sometimes arise in consequence of a 

 bacillus being found which, while giving a number of the 

 characteristics of either one or the other, fails to give some of 

 the characteristic tests, or only gives them very slowly. This is 

 especially true of organisms related to the b. coli. It has 

 consequently become common to speak of the typhoid group 

 and the coli group in order that such varieties may be included. 



Pathological Changes in Typhoid Fever. Here we confine 

 our attention solely to the bacteriological aspects of the disease. 

 The inflammation and ulceration in the Peyer's patches and 

 solitary glands of the intestine are the central features. In the 

 early stage there is produced an acute inflammatory condition, 

 attended with extensive leucocytic emigration and sometimes 

 with small haemorrhages. At this period the typhoid bacilli are 

 most numerous in the patches, groups being easily found between 

 the cells. The subsequent necrosis is evidently in chief part the 

 result of the action of the toxic products of the bacilli, which 

 gradually disappear from their former positions, though they 

 may still be found in the deeper tissues and at the spreading 

 margin of the necrosed area. They also occur in the lymphatic 

 spaces of the muscular coat. It is to be remarked that 

 the number of the ulcers arising in the course of a case bears no 

 relation to its severity. Small ulcers may occur in the lymphoid 

 follicles of the large intestine. 



The mesenteric glands corresponding to the affected part of 

 the intestine are usually enlarged, sometimes to a very great 

 extent, the whole mesentery being filled with glandular masses. 

 In such glands there may be acute inflammation, and occasionally 

 necrosis in patches occurs. Sometimes on section the glands 

 are of a pale-yellowish colour, the contents being diffluent and 

 consisting largely of leucocytes. Typhoid bacilli may be isolated 

 both from the glands and the lymphatics connected with them, 

 but the b. coli is in addition often present. 



The spleen is enlarged, on section usually of a fairly firm 

 consistence, of a reddish-pink colour, and in a state of congestion. 



