34 STORRS AGRICULTURAL EXPERIMENT STATION. 
Group IV. Neutral bacteria. This is the least satisfac- 
torily determined of all our types. It includes the colonies 
that show no acid reaction and no distinctive characters. ‘They 
are usually opaque, and grow readily both upon the surface of 
gelatin and below. Such characters are mostly negative, and it 
is to be expected that the group will include a considerable vari- 
ety of species. We have isolated and studied a large number of 
these, and find several distinct bacteria that are grouped under 
this type of colony. Some are cocci, some are rods. ‘They 
include Nos. 194, 198, and 205 of our published list (An. Rep. 
of Storrs Exp. Sta., 1895) and some other species which will 
be described in a later report. From the standpoint of their 
relations to milk they are of little importance, since they 
agree in having no noticeable effect upon milk under any con- 
ditions. We regard them, therefore, as neutral species. As 
seen from the following tables, they always comprise a large 
percentage of the bacteria in fresh milk and in older milk which 
has been kept at a low temperature. Whether they are of 
significance from a hygienic standpoint we have not yet deter- 
mined. Experiments are being undertaken at the present time 
to determine whether these organisms have any pathogenic 
properties. No pathogenic action upon guinea pigs has yet 
been determined, but the work is still too incomplete to justify 
any final conclusions. From the dairyman’s standpoint this 
group is quite neutral, since it produces no effect upon dairy 
products. Whether any members of the group are significant 
from the standpoint of the wholesomeness of the milk remains 
for further experiments todetermine. In our discussion of the 
results, given in the following pages, we shall refer to this 
group as the neutral bacteria. 
Group V. Yellow bacteria. ‘This group includes colonies 
with a brilliant yellow color.. Such a general description will 
naturally include many different species of bacteria, but nearly 
all those found in milk, in this vicinity, which produce the 
yellow color prove to be Sarcina. We have isolated many col- 
onies of this type, and found them in nearly every case of the 
Sarcina type. The group is of little importance for our study, 
since, although nearly always present in small numbers at the 
outset, they almost universally disappear after a few hours, and 
