CREAM-RIPENING. 213 
it a tryptic ferment, because it is similar in its action to the 
trypsin produced by the digesting glands. The putrefactive 
germs ordinarily act upon the nitrogenous matter of cream, 
as described above. 
2. The milk-sugar in cream is present in a perfect solution, 
and consequently it is thought that bacteria are able to utilize 
it as food directly. The typical lactic-acid-producing germs 
cause the milk-sugar to split up into lactic acid chiefly, accord- 
ing to the following equation: 
C12H22011 + H20 = 4C3H603. 
Milk-sugar. Lactic acid. 
There are a number of germs which are able to produce 
lactic acid from milk-sugar, but practically all of them, so far 
as known, produce other by-products besides the lactic acid. 
Some germs produce much lactic acid and a small amount of 
other by-products, while other germs produce little lactic acid 
and large amounts of several other by-products. Some of them 
break up the milk-sugar and change it into lactic acid and car- 
bonic gas. Other species produce lactic acid and alcohol. 
This latter species Grottenfelt claims to be closely associated 
with the production of flavoring substances in butter. Different 
kinds of gases, such as nitrogen, hydrogen, carbonic-acid gas, 
and marsh-gas are also formed. 
It is doubtful whether there are any germs which are able 
to transform milk-sugar entirely into lactic acid. If such were 
the case, 1 gram of milk-sugar would produce 1 gram of lactic 
acid. According * to some experiments carried on by one of 
the authors, .8 of a gram was the maximum amount of acid 
developed from 1 gram of milk-sugar, and .5% is the average 
amount of acid developed from 1 gram of milk-sugar. In the 
experiments, efforts were made to have the typical lactic-acid 
ferments present in the cream. The following table may prove 
of some interest: 
* Chemical Changes during Cream Ripening. (Thesis I. S. C.) 
