THE HARD CHEESES 213 
usually none left except the lactic acid bacteria. At first the 
predominant organisms are of the Bact. lactis acidi type; later 
the B. Bulgaricus type becomes most numerous. While there are 
variations in the bacteria in different kinds of cheese and in differ- 
ent specimens of the same variety, the above represents the general 
history of their growth, and in all cases it appears that the lactic 
acid organisms are finally found alone. 
It must be confessed that we do not yet know very much about 
the part bacteria play in the ripening of the hard cheeses. That 
they are necessary to the ripening is proved by the fact that cheeses 
do not ripen normally when they are ripened in chloroform vapor, 
which prevents bacteria growth, but allows the enzyme action to 
continue as usual. Although some of the digestive changes go on 
as usual in these cheeses, the ripening does not become complete, 
and the cheeses never develop either the same final chemical char- 
acter or the flavors of cheeses in which the bacteria have had an 
opportunity for growth. 
Chemical Action of Bacteria—When cheese-ripening was 
first studied, it was believed to be primarily due to the action of 
bacteria. We have already seen that certain kinds of bacteria 
have the power of changing casein to peptone—the liquefying type 
—and this change in the cheese-ripening was at first supposed to be 
due to the growth of these peptonizing bacteria. But later it be- 
came evident that the liquetying bacteria are not common in 
cheeses, especially in the better grades. If present at the begin- 
ning they rapidly decrease in numbers, until they almost or entirely 
disappear, a fact which forced the conclusion that they cannot con- 
tribute materially to the ripening of cheeses. More recently, it 
has been claimed that certain “‘acid liquefiers”—+.e., peptonizing 
bacteria that at the same time produce acid—are intimately con- 
nected with the ripening. But there does not yet appear to be 
much evidence for this. 
These facts led to a suggestion that the ripening is due really to 
the lactic acid bacteria. These do not liquefy gelatin and do not 
