CHAPTEE XV. 



TYPHOID FEVER BACILLI ALLIED TO THE 

 TYPHOID BACILLUS. 



Introductory. The organism now known as the bacillus 

 typhosus was first described in 1880-1 by Eberth, who observed 

 its microscopic appearance in the intestinal ulcers and in the 

 spleen in cases of typhoid fever (German, Abdominaltyphus). 

 It was first isolated (from the spleen) in 1884 by Gaffky, and its 

 cultural characters were then investigated. In 1885 Escherich 

 observed a bacillus, now known as the bacillus coli communis, 

 which occurs in the normal intestine, and which both micro- 

 scopically and culturally closely resembles the typhoid bacillus. 

 Ordinarily the b. coli is no doubt a harmless saprophyte, but 

 under experimental conditions in animals and also naturally in 

 man it may manifest pathogenic properties. Investigation has 

 shown that these two bacilli belong to a widespread group 

 of organisms isolated from various disease conditions, chiefly 

 of the intestine, which all bear close resemblances to one 

 another, and whose differentiation is often a matter of consider- 

 able difficulty. Other members of this group are the para- 

 typhoid bacillus, the organism of bacillary dysentery, the b. 

 enteritidis of Gaertner, the psittacosis bacillus, and the bacillus 

 of hog cholera. 



The general characters of the group are as follows : the 

 organisms, which are microscopically indistinguishable, are thin 

 non-sporing bacilli, which in cultures often show variation in 

 length ; they are mostly motile, but this quality varies in differ- 

 ent members ; they possess flagella springing from all round 

 the bacillus ; they stain with ordinary dyes, and are all Gram- 

 negative ; they are all facultative anaerobes, i.e. they grow best 

 in the presence of oxygen, but can tolerate its absence ; in 

 growth characters on ordinary media they closely resemble one 

 another, and, generally speaking, they do not liquefy gelatin; 

 they show wide differences in fermentative capacities, and are 

 chiefly to be distinguished by their immunity reactions. 



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