BACILLUS COLI COMMUNIS 389 



bacilli are the observation of their fermentative action upon carbohy- 

 drate media, and their agglutinating reactions in immune sera. These 

 points will be alluded to in the description of the individual microor- 

 ganisms, and will be again summarized in the differential tables given 

 at the end of the chapters dealing with this group. 



BACILLUS COLI COMMUNIS AND MEMBERS OF THE COLON 



BACILLUS GROUP 



Under the name of "colon bacilli" are grouped a number of bac- 

 terial varieties differing from one another somewhat in minor character- 

 istics, but corresponding in certain cardinal points which stamp them 

 as close relatives and amply warrant their consideration under one 

 heading. While usually Uving as harmless parasites upon the animal 

 and human body, and capable of leading a purely saprophytic existence, 

 they may, nevertheless, under certain circumstances become pathogenic 

 and thus, both culturally and in their pathological significance, form a 

 link between pure saprophytes like Bacillus lactis aerogenes, on the 

 one hand, and the more strictly pathpgenic Gram-negative bacilli of 

 the paratyphoid, typhoid, and dysentery groups, on the other. As a 

 type of the group we may consider in detail its most prominent and 

 thoroughly studied member. Bacillus coli communis. 



BACILLUS COLI COMMUNIS 



This microorganism was seen and described by Buchner^ in 1885. 

 It was thoroughly studied in the years ipimediately following, especially 

 by Escherich,^ in connection with the intestinal contents of infants. 



Morphology. — Bacillus coli communis is a short, plump rod about 

 1-3 micra long, and varying in thickness from one-third to one-fifth 

 of its length. Under varying conditions of cultivation, it may appear 

 to be more slender than this or shorter and even coccoid in form. In 

 stained preparations, it usually appears singly, but occasionally, may be 

 seen in short chains. It stains readily with the usual anilin dyes and 

 decolorizes by Gram's method. Spores are not formed. It is motile, and 

 flagella staining reveals eight or more flagella peripherally arranged. Its 

 motility is subject to wide variations. Young cultures, in the first gen- 



' Buchner, Arch. f. Hyg., 3, 1885. 



'Escherich, "Die Darmbakt. des Sauglings," Stuttgart, 1886; Cent. f. Bakt., 1, 

 1887. 



