i6o 



C.-E. A. WiNSLOw AND Anne F. Rogers 



judgment depend directly on other properties, such as the general 

 vigor of growth and the size of the cell aggregates. Both turbidity 

 and sediment vary markedly with the age of the culture; what is 

 first turbidity later settles to form sediment, as the waste products 

 of the bacteria check their development. The amount of either 

 depends on the activity of growth. A constant difference often appears 

 between cultures which early in the course of development show 

 considerable turbidity with little or no sediment, and those which 

 almost at once develop a heavy sediment v/ith colony-like masses 



.6 



.5 6 .9 1.2 1.5 1.8 2.1 2.4 2.7 5.0 



Fig. 2. — Acid production of 500 cocci; in dextrose broth 



and lactose broth = 



AbscissaE^ acidity in per cent normal. Ordinates, number of cultures. 



of growth cHnging to the walls of the tube. This difference, how- 

 ever, appears to be correlated with the growth-form and general 

 vigor of the coccus. Organisms of the Streptococcus type with cells 

 separating readily, which show faint surface growth, produce chiefly 

 turbidity; while organisms like Sarcina with large cell aggregates 

 and rich surface growths, show hea\y sediment. 



Gelatin plates. — Minute differences in the macroscopic and 

 microscopic appearance of colonies on gelatin are given great 



