BACTERIA OF MILK 53) 
the curd is clear. Being commonly concerned in the 
souring of milk and producing principally lactic acid, 
the organisms of this type are known as the true lactic 
acid bacteria. The Streptococcus lacticus must not be 
confused with the mastitis streptococci (Fig. 6), which 
also ferment lactose and have other corresponding char- 
acteristics. The latter organisms grow in long, inter- 
twined chains, the individual members of which are rec- 
tangular or oval in form, with the long axis at right 
Pps jacliom Ue Radaiun (alee |= Cablalaaaeg ahititugaliting jail from 6 
aoe 
angles to the length of the chain. On agar, they form 
extremely minute, punctiform, brownish colonies. 
The Bacteriwm acidi lactict (Hueppe), also called the 
Bacillus lactis aerogenes, is frequently concerned in the 
spontaneous souring of milk, usually in association with 
the Streptococcus lacticus. This is a short, plump, non- 
motile bacterium which is closely related to the coli-aero- 
genes group of bacteria and may be regarded as the most 
active acid-forming member of that group. It grows 
upon the surface of solid media, forming thin, partially 
translucent, leaf-shaped colonies, or round semi-globular 
