10 BULLETIN 782, U. S. DEPARTMENT OF AGRICULTURE. 



ever, in cow feces, being found in 8 out of 14 samples examined and 

 and they comprised about 2.7 per cent of the total bacteria. Brush- 

 ings from the udders and flanks of cows also showed the presence of 

 the organisms. Alkali-forming bacteria were also found in very- 

 large numbers in unsterilized milk pails and cans. In one examina- 

 tion of a 10-gallon unsterilized milk can which was about to be 

 filled with milk, approximately 144,000,000 of these organisms were 

 found. 



From extensive studies as to the sources of the alkali-forming 

 bacteria found in milk it is believed that they are primarily soil 

 organisms. The fact that alkali-forming bacteria are present in soil 

 is further supported by the work of Temple (11), who states as a 

 result of his experiments that ''It is clear that soil Kacteria can use 

 sodium or potassium salts of organic acids in such a way as to have 

 one of the products sodium or potassium carbonate." Soil, how- 

 ever, can not be considered the only source of the alkali-forming 

 group of bacteria, for there are probably many organisms from other 

 sources which might fall into this group based oh their character- 

 istic milk reaction. 



MORPHOLOGY AND GROWTH. 



In the study of the alkali-forming bacteria no elaborate morpho- 

 logical determinations of the organisms were made. Microscopic 

 examination of 24-hour-old agar cultures showed that of 69 cultures 

 6 were cocci and 62 bacilli. In individual cultures the rod-shaped 

 organisms varied greatly in size and for that reason it was not con- 

 sidered advisable to subdivide this group further according to their 

 morphological characteristics. None of the organisms were spore 

 formers. 



The optimum temperature of this group of alkali-forming bacteria 

 isolated from milk was found to be between 20° and 30° C, and 

 within this range they grew vigorously. There was some growth 

 below 20° C, but only slight growth above 30° C. In fact, 8 of the 

 cultures, when streaked on agar and incubated at 37° C. for 48 hours, 

 showed no growth, and 1 culture, No. 354, when inoculated into milk 

 and inoculated at 37° C, rapidly died out, so that on the ninth day 

 upon plating 1 cubic centimeter of this milk culture, no colonies 

 appeared on the plates. The organisms grew best under aerobic 

 conditions, but could also develop anaerobically on certain media. 

 No growth was observed under anaerobic conditions in a synthetic 

 medium containing sodium-ammonium phosphate as a source of 

 nitrogen and the salt or an organic acid as the only source of carbon. 

 The majority of this group of organisms appeared on agar plants as 

 a moist, white growth, but there were 6 fluorescent, 2 pink, and 1 

 yellow culture in the collection. The most noticeable feature of the 



