226 AGRICULTURAL BACTERIOLOGY. 



THE CAUSE OF CREAM-RIPENING. 



The chief agency in the ripening process is the growth of 

 bacteria. Many of the bacteria in the milk collect in the 

 cream, and, during the ripening period, have an opportunity to 

 multiply rapidly. The cream is kept at a temperature which 

 favors their growth, and at the end of the ripening they are 

 present in surprising numbers. Two actual experiments in 

 cream-ripening will best indicate the growth of bacteria in the 

 ripening of cream. The two samples of cream which gave the 

 following results were collected in cold winter weather, when 

 the number of bacteria was small at the outset and the ripen- 

 ing very slow. 



No. OF BACTERIA PER c.c. 



At beginning of Half ripened. Fully ripened, 



ripening. 



1st expt., 309,000 300,000,000 1,500,000,000 

 2d expt., 44,000 303,000,000 1,300,000,000 



The cream giving the highest numbers was somewhat over 

 ripened and the numbers somewhat large. Normally ripened 

 cream usually has from 300,000,000 to 600,000,000 bacteria 

 per c.c. 



These numbers are inconceivably great, far surpassing the 

 numbers found in sewage, or indeed, in any other natural ma- 

 terial where bacterial analyses have been made. 



Such rapid multiplication of bacteria clearly shows that the 

 chief feature of cream-ripening must be the growth of bacteria. 



Whether this process is wholly one of bacterial growth is 

 not certain. Babcock and Russell have shown that certain 

 enzymes are present in milk, and that they play an important 

 part in the ripening of cheese. If such enzymes are present 

 in the cream they may have a share also in cream-ripening. 

 At present, however, we have no evidence of this, but the evi- 

 dence of the agency of bacteria in the process is abundant and 

 conclusive. At all events, no one questions that the flavor 



