6 4 



RELATIONSHIPS OF THE COCCACE^: 



per cent is the optimum acidity for a majority of these 

 organisms, and that an excess of acidity over this 

 amount is more generally fatal than an alkalin reaction. 



NUMBER OF ORGANISMS SHOWING MAXIMUM GROWTH AND 



DEEPEST COLOR AT VARIOUS DEGREES OP ACIDITY. 



33 Cultures of Cocci. 



8 organisms showed no color. 



Relation to free oxygen. The Committee on Stand- 

 ard Methods (1905) recommends that the relation of 

 bacteria to oxygen be studied by the comparison of cul- 

 tures made under normal and under anaerobic con- 

 ditions. A preliminary study of fifty cultures, made 

 in this way, led to the belief that such a procedure 

 is unnecessary among the cocci. It became evident 

 that there are two main types of these 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 differ- 

 ence between the anaerobic cultures of the cocci. Some 

 forms which grow distinctly, but faintly, without air grow 

 no better with air, while others which almost wholly fail 



