36 BULLETIN 782, U. S. DEPARTMENT OF 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 cojatamination. 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 sHmy 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-fo'rming 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 

 foimd 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 rafiinose. 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. 



