TYPES OF BACTERIA FOUND IN MILK 159 
into a hard curd, without any trace of gas bubbles, and without the 
separation of whey: it has a clean, sharp taste, and no odor (Fig. 
30, 6). This type of curdling has been recognized as a desirable 
one by the dairyman, since it is most favorable for dairy processes 
Fic. 30.—Showing the action of different types of bacteria upon milk. a, the 
aerobic type (Bact. aerogenes); b, the anaerobic type (Bact. lactis acidi) ; c and d, the 
peptonizing type, with the curd in different stages of digestion. 
and is consistent with the production of the best grades of butter 
and cheese. This organism grows readily at temperatures from 
60° to 100°F., growing more rapidly at higher temperatures. At 
a temperature of about 70° it grows with great rapidity, and at 
this temperature it seems to be more vigorous than any other 
bacterium ordinarily found in milk. For this reason, as we shall 
