106 STORRS AGRICULTURAL EXPERIMENT STATION. 
meaning whatsoever among bacteria. Our names, therefore, 
refer to groups under which there are in some cases many 
sub-varieties, in other cases few and in some cases uo sub- 
varieties. From the standpoint of practical dairying the sub- 
varieties are sometimes of more significance than the general 
type. For example, under the head of Bacterium lactis acidi 
there are certainly a number of varieties differing in re- 
spects which are of extreme importance to the dairyman. 
They differ in the amount of acid they produce and in their 
power of curdling milk. So, too, under the head of Bacterium 
lactis aerogenes we have clearly a group of organisms differing 
in many important characters. Among these characters there 
is wide difference in the extent of the gas production; some 
cultures producing only a small amount of gas, others produc- 
ing gas in prodigious quantities. While these variations in the 
amount of gas cannot, in our opinion, be regarded as points by 
which the group should be separated from each other in a 
scheme of classification, they are of the highest importance to 
the dairyman. The variety which produces a small amount of 
gas would be consistent with the best dairy products, while the 
presence of the other variety would totally ruin a lot of butter 
and more surely ruin a lot of cheese. These sub-varieties, in 
short, are of extreme importance to dairymen, and the careful 
study of these varieties is a problem which should be con- 
sidered carefully in the future; but in a general classification of 
bacteria it is, in our opinion, at present quite impossible to rec- 
ognize all of these types by name, and our present plan is, 
therefore, only to group them as varieties under the general 
group name. 
METHOD OF STUDY AND DESCRIPTION. 
A few words are needed as to the method of obtaining the 
data tabulated in our descriptions. The zso/atzon of the bacteria 
is usually accomplished by the use of litmus gelatine. The pre- 
paration of this litmus gelatine has been described in a former 
publication. (Bacteria in Milk and its Products, P. Blakistons 
Sons.) This has been used because our experience has shown 
that it gives a better differentiation of colonies than other solid 
media. After isolation the cultures are purified by the ordinary 
' 
