66 STORRS AGRICULTURAL EXPERIMENT STATION. 
GROUPS OF MILK BACTERIA. 
A long study of the ordinary milk bacteria of this locality 
has shown us that they may quite satisfactorily be divided into 
several groups. ‘This grouping has been selected because each 
of the groups is capable of tolerably sharp differentiation upon 
the litmus gelatin plates. Although the basis of the arrange- 
ment is their action upon litmus gelatin, it is found that the 
groups selected have each a special relation to milk and are 
thus significant in the consideration of dairy problenis. 
The groups into which we have divided the bacteria are as 
follows: 
Group I. Sact. lactis acidi group. ‘This is the most widely 
distributed of all lactic bacteria and has been fully described in 
other places. It appears upon our plates as a small opaque 
colony, growing under the surface only, and with its periphery 
marked by minute spines showing with a 1 inch objective. 
The colony is red and is surrounded by a red halo. We have 
isolated large numbers of these colonies from the plates and 
carefully studied them by culture methods. ‘They all prove to 
be BL. lactis acidz, although showing variation in their power. of 
curdling milk, some curdling it rapidly, others slowly, and 
others not at all (See paper by Hsten in Rep. of this Station, 
1896). They are usually very easily differentiated upon our 
plates and are few in numbers in fresh milk but abundant in 
old milk—No. 206 of our classified list. 
Group II. Bact. lactis acidi 7. group. ‘This is represented 
apparently by a single species. It is very closely related to 
Group I. and has much the same action upon the milk. It 
differs from Group I. chiefly in its colony on litmus gelatin, 
which is very small, usually invisible to the naked eye, and 
quite transparent. It is more feebly acid than the colony of 
Group I. and lacks the characteristic spines. It is rarely found 
in fresh milk, but is common in old milk; especially in some 
samples kept at high temperatures. The group seems to be 
sharply differentiated from others on the plates, and the many 
colonies isolated all prove to be the same species, No. 202 of 
our classified list. 
Group III. Bact. lactis aerogenes group. The typical spe- 
cies of this group is B. dactzs aerogenes (Hscherich), which is a — 

