COMPARATIVE STUDY OF THE COCCI 63 



of isomeric compounds of different rotating power was 

 characteristic of certain bacteria. 



Action upon nitrates. Data with regard to the reduc- 

 tion of nitrates by the cocci are extremely meager, the 

 presence or absence of this character being recorded in 

 very few of the published descriptions. It seems, how- 

 ever, to have a fair degree of definiteness, and we have 

 included it as a qualitative test in our routine. Each 

 organism was inoculated into a series of ten tubes of 

 standard nitrate solution. After seven days' growth at 20 

 degrees the tubes were tested for nitrites and ammonia 

 in the regular way prescribed by the Committee on 

 Standard Methods (1905). The test for nitrates was 

 omitted after it was found that all the cultures, out of a 

 considerable series tested, gave positive results, without 

 exception. 



Production of indol. A preliminary study of some 

 fifty cultures showed no production of indol in any 

 case, and an examination of the literature of the cocci 

 indicates that this property is very rare, if it ever occurs, 

 in this group. It was therefore omitted from our routine. 



Inhibition of growth by acidity and alkalinity of 

 media. This character is of considerable importance 

 and warrants careful study, but it is obviously a difficult 

 property to observe in a large series of cultures, and we 

 have not attempted to use it in the present investigation. 

 A preliminary examination of 33 cultures, the results of 

 which are shown in the table below, indicated that 1 



