512 PA THOGENIC BA C TERIA . 



should be important evidence of their separate individ- 

 uality. 



I have no doubt that the Bacillus coli communis 

 is not a single species of bacteria, but is a name ap- 

 plied to a group whose individual differences are too 

 similar to enable us to differentiate them. This opin- 

 ion seems to be shared by other bacteriologists, some of 

 whom have attempted a separation into groups, types, or 

 families. 



In order to establish a type species of the Bacillus coli 

 communis, Smith 1 says: 



" I would suggest that those forms be regarded as true 

 to this species which grow on gelatin in the form of deli- 

 cate, bluish, or more opaque, whitish expansions with 

 irregular margin, which are actively motile when exam- 

 ined in the hanging drop from young surface-colonies 

 taken from gelatin plates which coagulate milk within 

 a few days; grow upon potato, either as a rich-pale or 

 brownish-yellow deposit, or merely as a glistening, barely 

 recognizable layer, and which give a distinct indol reac- 

 tion. Their behavior in the fermentation-tube must 

 conform to the following scheme: 



' ' Variety a : 



"One per cent, dextrose-bouillon (at 37 C). Total 

 gas approximately }4\ HC0 2 approximately yi\ reaction 

 strongly acid. 



" One per cent, lactose-bouillon: as in dextrose-bouil- 

 lon (with slight variations). 



"One per cent, saccharose-bouillon; gas-production 

 slower than the preceding, lasting from seven to four- 

 teen days. Total gas about 2 / 3 ; HC0 2 nearly %. The 

 final reaction in the bulb may be slightly acid or alkaline, 

 according to the rate of gas-production. 



"Variety ft: 



" The same in all respects, excepting as to its behavior 

 in saccharose-bouillon; neither gas nor acids are formed 

 in it." 



1 American "Journal of the Medical Sciences, 1895, IIO, p. 287. 



