178 PATHOGENIC BACTERIA 



derives its name. The group of bacteria, the typho- 

 colon series, to which this organism belongs and of which 

 it and the typhoid bacillus are the most conspicuous 

 representatives, embraces many species, subspecies, and 

 varieties. A botanical and chemical classification satis- 

 factory to all authorities has not yet been made. It can 

 be said in general that all members of this group find 

 the intestinal tract a suitable place for life, some under 

 normal, others under pathological conditions. Old 

 classifications of the typhocolon group admitted only 

 organisms capable of motion, but some later observers 

 include many non-motile, and even encapsulated forms. 

 Inasmuch as a very close separation on the basis of 

 technicalities is not necessary in this work, it has 

 been deemed best to choose the principal clearly defined 

 species for description. Such descriptions permit of 

 extension in a general way to the nearest congeners, 

 and therefore we may say that we are considering 

 types. The typhoid and paratyphoid bacilli have 

 been sufficiently described in Chapter IX. 



The Colon Bacillus. The colon bacillus proper, 

 called also the Bacillus coli communis, is a non-spore- 

 bearing, sluggishly motile, delicate rod, measuring 



from 2 o ToT, to s (M) o inch in len S th and 6W6 o to JooFo 

 inch in width. It appears when stained as a single 



rod usually, but occasionally in pairs or short chains. 

 It takes the laboratory dyes with ease, usually more 

 deeply near its rounded ends. It moves by flagella 

 arranged all about the cell wall. It grows with ease 

 artificially, best in the presence of oxygen, but also 

 in its absence. Development will occur at any tem- 

 perature from 10 to 43 C. or 50 to 108 F. It pro- 



