VARIETIES OF B. COLI 395 



With regard to sugars, MacConkey concludes that in the differentiation 

 of the lactose fermenters, the only sugars necessary are lactose, saccharose, 

 dulcite, adonite, inulin, inosite, and mannite. Using these, a prelimin- 

 ary classification can be made from the actions on cane-sugar and dulcite, 

 and four groups are constituted : I. Organisms not affecting either cane- 

 sugar or dulcite. II. Organisms having no action on cane-sugar, but 

 fermenting, dulcite. III. Organisms fermenting both cane-sugar and 

 dulcite. IV. Organisms fermenting cane-sugar, but having no action on 

 dulcite. Of the first, the bacillus acidi lactici of Hiippe may be taken as 

 a type ; of the second, the bacillus coli communis of Escherich ; of the 

 third, bacillus Friedlander ; of the fourth, the bacillus lactis aerogenes 

 and the bacillus cloacse. Group IV. is further subdivided into sub-group 

 1, in which there is no liquefaction of gelatin and an absence of the 

 Voges and Proskauer reaction ; 2, with no liquefaction of gelatin, presence 

 of Voges and Proskauer's reaction (bacillus lactis aerogenes) ; 3, with 

 liquefaction of gelatin, presence of Voges and Proskauer's reaction (bacillus 

 cloacae) ; 4, with liquefaction of gelatin and production of a yellow pigment. 

 Taking the properties named as type characteristics, the great mass of 

 lactose fermenters can be further differentiated by the application of the 

 other sugar tests. It is well to refer any organism found as belonging 

 to one or other of the types, as in most cases no name has been assigned. 

 Examples are constantly met with in work on water or fajcal contents. 



Although many of the named varieties were originally described in 

 connection with other bacterial processes, all these bacteria are of frequent 

 occurrence, especially in the human and animal intestine. As in the 

 case of the members of the food-poisoning group, great difficulty has been 

 experienced in identifying the types from mere description, and consider- 

 able complication has arisen from the fact that before the elaboration 

 of the modern differentiation technique, different observers identified 

 organisms as belonging to a classical type, which have now been found 

 not to conform in properties with the historic strains ; here again, it is 

 now customary during classification work to have at hand such historic 

 strains in order that comparative parallel observations may be made. 



With regard to the type strains, a few words may be added. The 

 original bacillus coli communis of Escherich was isolated from the 

 intestine of newly-born infants in connection with the first appearance 

 of bacteria in the alimentary tract. About the same time, an organism 

 now known as the bacillus neapolitanus was obtained by Emmerich in 

 an outbreak of choleraic disease in Naples, and this organism was looked 

 upon as identical with Escherich's bacillus, but it ferments saccharose, 

 on which Escherich's has no effect. The bacillus acidi lactici of Huppe 

 was stated by this observer to be the chief cause of the souring of milk. 

 It is now known that a large number of organisms of the same type, but 

 differing slightly in cultural characters, are concerned in this process, 

 and, as a matter of fact, MacConkey found the presence of the classical 

 strain to he relatively infrequent in milk. The bacillus lactis aerogenes 

 was originally described by Escherich, in connection with his work on 

 the bacteriology of the intestine in children, as an organism differing 

 from the ordinary milk-souring bacteria by its producing gas from milk 

 in the absence of. air. Although it is a free gas-producer, this property 

 is not specific for it, and within recent years it has attracted attention 

 chiefly from its apparently being closely allied to the bacillus pneumonia 

 of Friedlander. Like the latter, this organism is stated when injected 

 into animals to appear in » capsulated form. Another member of this 



