134 STORRS AGRICULTURAL EXPERIMENT STATION. 
WHITE, ACID-PRODUCING BACTERIA. 
These are immensely numerous. They are the common cause of the souring 
of milk, and since this phenomenon is practically universal, it follows that these 
bacteria are equally widely distributed. This group contains the dairy bacteria 
par excellence. By this is not meant that these are most abundant around the 
barn or in fresh milk. As pointed out elsewhere, they are not common in the 
udder of cows, and are usually present only in small numbers in freshly drawn 
milk. But they are so much better adapted to life in milk that they soon 
become more abundant than all other bacteria put together. Thus in older 
samples of milk they are by far the most common. 
We have studied hundreds of cultures belonging to this general type, obtained 
from all over this country, as well as from several localities in Europe. Among 
this large series of samples we have found endless variations. There is hardly 
a characteristic which does not show wide variations in the numerous cultures 
studied. They include such widely different types that it is hardly proper to 
put them into one group, but to arrange any satisfactory subordinate grouping 
is almost an impossibility. This might be done by selecting almost any of the 
characteristics of the type and arranging the different cultures according to its 
variations. The most satisfactory arrangement as appeared to us is to divide 
them according to their power of producing a surface growth on various media. 
This is not a sharp character, but it presents at least two extremes which may 
be clearly separated. 
Heinemann (Cent. f. Bac. u., Par. II., XVI., p. 538, 1896) doubts whether 
the common lactic organisms should be called by the name Bacterium, believ- 
ing that they are really all Streptococci. We are inclined to doubt the correct- 
ness of this view, and prefer to retain the long accepted nomenclature. 
Bact. lactis acidi Leichmann. This is the common cause of sour milk. 
Among the many scores of organisms of this type which we have studied 
we have tried to recognize some groups worthy to be called varieties. Whether 
this is possible is uncertain, since all are connected by slight intermediate 
gradations. We recognize, however, the following: 
Bact. lactis acidi, type. 
Morphology.—A bacterium. Size, .7u-1.24x .5u-.84. Sometimes so short 
as to be described as a streptococcus, and some cultures are very clearly cocci. 
(See p. 114.) There is no motility, no spores, and no long chains. Gram stain 
is positive. 
Gelatine colony.—Colonies are small points, rather opaque, not characteristic. 
They are almost wholly under the surface, and never typically grow on the sur- 
face. In /ztmus gelatine they are rather dense, strongly acid, and frequently, 
though not always, surrounded by minute, irregular spines on the edge. This 
type of colony can usually be detected with a little experience, and is the most 
characteristic feature of the type. ; 
Gelatine stab.—A granular or linear needle growth, and no surface growth. 
Agar streak.—TVhere is no growth, or one that is scarcely visible. On milk 
agar it grows rather better, but at best it is very scanty. 
