SUBFAMILIES AND GENERA OF COCCACE^ 105 



The chromogenic type center for both micrococci and 

 sarcinae lies in the lighter shades of the Medium Cadmium 

 Yellow (see frontispiece). Both are typically saprophytic 

 in habit; 73 per cent of our micrococci and 76 per 

 cent of our sarcinae were from water, earth, or air. They 

 are generally Gram-negative; only 22 and 23 per cent, 

 respectively, gave two successive, positive results. In 

 fermentative power micrococci and sarcinae correspond 

 closely, as indicated in Figure II. In each case a very 

 faintly acid or neutral reaction was the general rule. A 

 few strains, about 20 per cent in each case, formed an 

 acidity over .004 normal in dextrose broth, and about 10 

 per cent exceeded a similar limit in lactose broth. In 

 relation to temperature, and in chromogenic power also, 

 micrococci and sarcinae agree. In all these respects the 

 parallelism of these two series of the yellow cocci empha- 

 sizes the differences which separate them both from the 

 Paracoccaceae. 



Two characters only appear, from a careful comparison, 

 to distinguish the packet-forming and non-packet-forming 

 yellow cocci. The sarcinae produce, on the whole, more 

 vigorous surface growths than the micrococci. Thirty- 

 three per cent of the former produced a growth desig- 

 nated as "very heavy" in our observations; while only 

 8 per cent of the micrococci showed a growth of this kind. 

 And in gelatin cultures the sarcinae exert a more vigorous 

 action than the micrococci, as appears in Figure III. 

 A difference of the latter sort may be due to the pro- 



