Generic Characters in the Coccaceae 167 



Relation to free oxygen. — The Committee on Standard Methods 

 (1905) recommends that the relation of bacteria to oxygen be studied 

 by the comparison of cuhures made under normal, and under anae- 

 robic, conditions. A preliminary study of 50 cultures made in this 

 way led to the belief that such a procedure is unnecessary among 

 the cocci. All but two of the cultures studied showed some growth 

 under anaerobic conditions, but the growth was in most cases meager. 

 It became evident that there are two main types of organisms: those 

 which, like Streptococcus, grow only feebly on the surface of aerobic 

 agar, and which grow equally well under anaerobic conditions; and 

 those, like Sarcina, which form abundant surface growths under 

 aerobic conditions, and under anaerobic conditions grow feebly 

 like Streptococci. In other words, there is little difference between 

 the anaerobic cultures of the cocci. Therefore, for purposes of classi" 

 fication we have considered the study of the aerobic surface growth 

 a sufficient measure of the relation to ^ree oxygen, as well as of 

 general vigor. The five grades recorded under vigor of surface 

 growth correspond fairly well to four grades of aerobiosis, from 

 forms anaerobic and facultatively aerobic, to forms which are strong 

 aerobes. 



Temperature relations. — There are two points of special importance 

 which ought to be determined in studying temperature relations, 

 the optimum temperature and the high death-point. The death- 

 point at extremely low temperatures is too indefinite to be attempted, 

 and the extreme limits of growth, although desirable data may be 

 omitted as less important than the other two properties. 



For the determination of the optimum temperature we first made 

 a series of preliminary studies by comparing agar cultures grown 

 at 10°, 20°, 37°, 45°, and 56°. We found two cultures growing bet- 

 ter at 20°, 18 developed equally well at 20° and 37°, 22 showed an 

 optimum at 37°, two grew equally well at 37° and 45°, and four grew 

 best at 45°. These conclusions refer only to the amount of growth, 

 color production being in most cases most active at 20°. From 

 these results we concluded that the information to be gained by cul- 

 tures grown below 20° and above 37° would be scarcely commensu- 

 rate with the labor involved, and we have limited our observation 

 to the comparison of growth and color production at 20° and 37°. 



