CLASSIFICATION OF DAIRY BACTERIA. P27 
Milk.—Rendered slightly acid, curdled, and later completely digested into a 
greenish-yellow liquid. 
Potato.—Scanty, thin, smooth, white. 
Grows at both 20° and 37°. Facultative anaerobic. 
M. lactis varians n. s. Yellow, liguefying, acid-producing Cocct. This is 
perhaps the most common and widely diffused type of coccus found in milk. 
We have found it in milk from many localities, and it is very abundant. It is 
frequently present in milk directly from the udder. It shows a wide range of 
variations affecting nearly every character. We have studied some scores of in- 
dependent cultures from different sources, and find that the different types 
grade into each other by such slight differences that we have no hesitation in 
putting them all together asone type. This organism liquefies gelatine, but in 
some cases so slowly as to form only a dry pit. From this it is only a step to 
a non-liquefying form. We, therefore, are inclined to believe that this type is 
identical with, or at least closely allied to, W/. lactis aureus (p. 112). The 
characters as we have studied them agree essentially with those of Staph. pyogenes 
aureus. Cultures of the latter organism, sent us by Retger, have been com- 
pared side by side with our cultures and no essential differences are seen. We 
are inclined to think, therefore, that our type is the common Staph. pyogenes 
aureus. In the description that follows the limits of variations will be given 
under each head and no attempt will be made to distinguish distinct varieties. 
Morphology.—Size, .4u-1.4u. Gram stain positive. 
Gelatine colony.—Deep colonies are opaque; surface colonies form white or 
yellowish beads or a slow liquefying colony With a clear liquid and a granular, 
mottled, irregular growth, distributed in the liquid. It is usually slightly acid 
in litmus gelatine, sometimes decidedly so, forming a bright red liquid colony. 
Gelatine stab.—Liquefaction is usually slow but sometimes rapid. It com- 
monly begins in from two to four days, but is never complete. In some cul- 
tures liquefaction is so slow that only a dry pit is formed, with a broken, 
yellow growth on its side. It is usually napiform. 
Agar streak.—A luxuriant growth, frequently tending to be rough, though 
never wrinkled. -It does not spread profusely. Its color is typically pale 
orange-yellow, but varies from this to nearly orange and to practically white. 
In the latter case this is quite indistinguishable from JZ. lactis albidus (p. 123). 
The agar growth may be dry or moist. 
Fermentation tubes.—All three sugars are rendered acid and growth appears 
in the closed arm. No gas is ever formed. Some cultures do not grow in the 
closed arm and some have failed to render lactose and saccharose acid. 
Bouillon.—A flocculent sediment is produced and a slight turbidity. Two 
cultures showed a granular pellicle. 
Milk.—Is always rendered acid and commonly curdled and digested with a 
yellow sediment. In the non-liquefying cultures the curdling may not appear 
nor any noticeable digestion. ‘ 
Potato.—Is usually luxuriant, though sometimes scanty, of a pale orange- 
yellow color, showing the same variations as mentioned in agar streak. It is 
frequently dry. 
Grows better at 37° than at 20°. Facultative anerobic. 
