PATHOLOGICAL CHANGES 373 



litmus milk slight acid production occurs ; in a time varying 

 from a few days to a month the acid change may be succeeded 

 by alkali production. Under ordinary circumstances, the typhoid 

 bacillus is incapable of producing indol in peptone-salt solution, 

 and does not alter neutral-red in lactose bouillon. 



A great many special tests were formerly in use in differ- 

 entiating the b. typhosus from the b. coli. The use of these 

 is not now so necessary, but the following may be described : 



The Media of Capaldi and Proskauer.The first of these ("No. 1 ") is 

 a medium free of albumin, in which b. coli grows well and freely produces 

 acid, while the typhoid bacillus hardly grows at all, and certainly will 

 produce no change in the reaction. Its composition is as follows : 

 asparagin '2 parts, mannite '2, sodium chloride "02, magnesium sulphate 

 "01, calcium chloride '02, potassium monophosphate '2, distilled water 

 to TOO parts. The second medium ("No. 2") contains albumin, and 

 in it the b. coli produces no acid, while the typhoid bacillus grows well 

 and produces an acid reaction. It consists of Witte's peptone 2 parts, 

 mannite '1, distilled water to 100 parts. After the constituents of each 

 medium are mixed and dissolved, it is steamed for one and a half hours 

 and then made neutral to litmus the first medium, being usually 

 naturally acid, by sodium hydrate, the second, being usually alkaline, by 

 citric acid. The medium is then filtered, filled into tubes containing 

 5 c.c., and these are sterilised. After incubation for twenty hours the 

 reaction of the infected medium is tested by adding litmus. 



The identification of the typhoid bacillus is best facilitated 

 by means of agglutination reactions which will be treated of 

 later (pp. 382, 406). 



Pathological Changes in Typhoid Fever. Here we confine 

 our attention solely to the bacteriological aspects of the disease. 

 The inflammation and ulceration in the Feyer's patclies 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 spread- 

 ing margin of the necrosed area. They also occur in the lym- 

 phatic 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 



