CHAPTER XV. 



TYPHOID FEVER— BACILLI ALLIED TO THE 

 TYPHOID BACILLUS. 



Introductory. — The organism now known as the bacillus 

 typhosus was first described in 1880-81 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 

 described what is 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. 

 While ordinarily the b. coli is a harmless saprophyte, under 

 experimental conditions in animals and also naturally in man it 

 may manifest pathogenic properties. These two bacilli belong 

 to a widespread group of organisms isolated from various disease 

 conditions, chiefly of the intestine, which bear close resemblances 

 to one another, and whose differentiation is often a matter of 

 considerable difficulty. Other members of this group are the 

 para-typhoid bacilli, the dysentery bacilli, the b. enteritidis of 

 Gaertner, the psittacosis bacillus, and the bacillus of hog cholera. 

 The general characters of the coli-typhoid group are as 

 follows : the organisms, which are microscopically indistinguish- 

 able, are thin non-sporing bacilli, which in cultures often show 

 variation in length ; they are mostly motile, "but this quality 

 varies in different members ; they possess flagella springing from 

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

 all Gram-negative ; they are all fa cultative 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 they do not liquefy gelatin; they 

 show wide differences in their actions on sugars, and a primary 

 classification of the group is based on the fact that while b. coli 

 produces acid and gas from lactose, none of the pathogenic 



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