TYPES OF BACTERIA FOUND IN MILK. 147 



bacterium ordinarily found in milk. For this reason, as we shall 

 presently see, milk kept at 70 becomes, in a short time, almost 

 completely filled with this species of bacterium at the expense of 

 all the others that might originally have been there. This type of 

 organism is a friend to the dairyman, unless he be a milk man who 

 wants to deliver his milk sweet. 



Fi<;. 31. Showing the action of different types of bacteria upon milk, a, the 

 aerobic type (Bact. aerogenes); b, the anaerobic type (Bad. acidi lactici); c and d, the 

 peptonizug type, with the curd in different stages of digestion. 



II. Bacterium aerogenes. This type of lactic acid organism is not 

 so abundant in milk as the first, although it may be found more or 

 less abundant in most samples of milk. Microscopically, it is 

 practically indistinguishable from the first variety, but it differs in 

 two pronounced points (Fig. 32). The first is that it grows luxuri- 

 antly in contact with the air or oxygen, while the first variety does 



