36 BULLETIN 782, U. S. DEPARTMENT OE AGRICULTURE. 
organisms of this group found in milk were principally soil bacteria 
introduced into milk largely from unsterilized utensils, with dust, 
or from the dirty hands of milkers. Cow feces may also play a small 
part in the contamination. In general, soil can not be considered 
the only source of these organisms, because there are many bacteria 
from other sources, which would be placed in this group on account 
of producing the characteristic milk reaction. 
3. Cultures of the bacteria included both cocci and bacilli which 
grew best aerobically at temperatures ranging from 20° to 30° C. 
When heated in milk for 30 minutes, the thermal death point of 
these organisms ranged from 60° to 65.6° C. No spores were ob- 
served. Most of the cultures produced a slimy growth on agar, several 
showed fluorescence and a few showed pigment formation. 
4. Sodium-ammonium phosphate was used as a source of nitrogen 
in the study of the alkali-forming bacteria. While the organisms 
could utilize nitrogen from numerous organic materials when suitable 
sources of carbon were supplied, either contained in them or supplied 
from other sources, it was found necessary in studying the fermenta- 
tion of test substances to have a definite source of nitrogen free from 
carbon. 
5. In studying the fermentation of test substances, nitrogen was 
supplied by sodium- ammonium phosphate, while the test substance 
furnished the carbon. The ordinary beef-extract broth was not 
found to be suitable for the determination of the fermentation of 
carbohydrates, because carbon was available either from the carbo- 
hydrate used or the organic-acid salts present in the beef-extract 
broth. It was possible, therefore, for a simultaneous acid (from the 
carbohydrate) and alkaline (from the organic-acid salts) fermenta- 
tion to take place, in which case the final reaction would depend on 
the rate of the two fermentations. It was often found that in beef- 
extract broth the acid fermentation was entirely masked by the 
alkali fermentation. To overcome this as far as possible a synthetic 
medium was used which contained a single source of nitrogen and 
single but different source of carbon. Dextrose was the most easily 
fermented of the carbohydrates tested. Of the 68 cultures examined 
44 fermented dextrose, 1 1 lactose, and 2 saccharose, while none fer- 
mented rafhnose. Dextrose and galactose were fermented to about 
the same extent and many media showed a high hydrogen-ion con- 
centration, while lactose and saccharose were fermented only slightly. 
In extract broth there was no evidence of a lactose fermentation — 
in fact, the reaction went alkaline — but in the synthetic medium a 
sight but distinct fermentation was observed. 
6. The monoatomic alcohols ethyl, propyl, and amyl were more 
readily fermented than the polyatomic alcohols mannite and glycerin. 
The alcohols tested were the only source of carbon in the sodium- 
ammonium-phosphate medium. 
