EXPERIMENT STATION BULLETINS. 



471 



Table XV shows that Strain II is affected very little if at all by the 

 peptone. The acidities of the peptone-milk are a little higher than those 

 of the plain milk, becanse the peptone has an acidity of its own, about 

 3°-4°, The difference in the fennenting capacities in the two duplicates 

 is within the limits of error. The rate of growth also shows no differ- 

 ence. The final acidity of the peptone-milk is about 8° higher than that 

 of the check, otherwise the four cultures are as much alike as can be 

 expected in parallel cultures. 



Quite different is the action of peptone upon Strain IV. The slow de- 

 velopment is illustrated by the fact tbat the milk cultures did not coagu- 

 late in 48 hours, and after 72 hours the acidity was lower than with 

 Strain II after 21 hours. The peptone-milk cultures, however, acidi- 

 fied much faster even than Strain II, and the final acidity is twice as 

 liigh as that of the plain milk culture. The counts of the bacteria show 

 about five times as many bacteria in the peptone-milk, indicating a faster 

 multiplication in the presence of peptone. This is substantiated by the 

 computation of -the rate of reproduction. The time required for one 

 cell to produce two cells in plain milk compared with peptone milk 

 is 118 against 99, 82 against 70 and 78 against 68 minutes in the three 

 experiments. In every case, the reproduction requires less time in the 

 presence of peptone. 



