TYPES OF BACTERIA FOUND IN MILK. 151 
different product from the original milk, since it no longer contains 
casein, but only the digested and dissolved products of casein. 
This softening and dissolving of the curd is so much like the diges- 
tion that goes on in the intestine of animals, that it has commonly 
been called digestion. The bacteria that produce it are also some- 
times called the peptonizing bacteria, since they produce peptones 
among the soluble products that come from the digested casein. 
Still another term is applied to these bacteria. One of the 
common culture media used in bacteriological work is solidified 
\ \ 
B C 
\j 
FIG. 35. Gelatin stab cultures. e,f, and g. show liquefaction; a, filiform; b, beaded; 
c, villous; d, arborescent; e, napiform; /, infundibuliform; g, stratiform. 
with gelatin. Now, many kinds of bacteria cause the solidified jelly 
to become liquid (Fig. 35E. F. G.). The liquefaction of the gelatin 
is due to the same enzyme that causes the digestion of the milk curd. 
Hence, we find that the bacteria that liquefy gelatin commonly 
have the power of dissolving milk curd. The term liquefiers is 
applied to them, since they liquefy both curdled milk and gelatin. 
This type of bacteria is very abundant, and in the number of kinds 
exceeds the number of lactic acid bacteria. They are found pro- 
fusely in the dairy, especially in the filth that gets into the milk. 
Practically every sample of fresh milk will contain them in greater 
or less numbers. But it is very doubtful whether this type of bacteria 
is of much or of any significance in ordinary daiiying. Although 
the varieties may be numerous and their number may be great in 
