HY R. GRElG-SillTH. 



39 



Races of Enterococcus, 



X Positive. — Negative reaction. 



The pliysiological characters of the bacteria which have no 

 action upon gelatine, wliich are negative to the Gram stain, 

 vvliich reduce nitrate to nitrite, and which form indol in peptone 

 salt solution, differ so gradually from one anotlier that it appears 

 probable that they have been derived from a common type or 

 ancestor, and have become altered by various conditions of 

 environment. It appears to be simply a question of research to 

 obtain all giaduations from an absolutely positive to an abso- 

 lutely negative race. It is therefore difficult to fix a race to any 

 one name. The absolutely positive races are undoubtedly Bac. 

 coli communis, but the absence of any one, or even more than 

 one positive character, is not sufficient to differentiate the race, 

 for the character may be only temporarily lost. Some work 

 which is in progress upon the permanency of these race- 

 characters shows that this is the case. One of the typical 

 characters of a bacterium is its motility, but an absence of 

 motility may have been noted in a faulty medium or at a wrong 

 time. For example, B^^ was non-motile at first, but after culti- 

 vation for some weeks in the laboratory, it became actively 

 motile. It therefore appears to be a mistake to include a race 

 under the name Bac. coli immobilis. The regeneration of the 

 one chaT:acter in the case of B indicates that, under favourable 

 circumstances, other negative characters may become positive. 



