ALKALI-FORMIISTG BACTERIA FOUND IN MILK, 9 



which was previously stated, namely, that the alkali-forming 

 bacteria produce an alkaline change in milk, due primarily to the 

 formation of carbonates or bicarbonates, resulting from the oxida- 

 tion of citric acid. After a long period of incubation there is a small 

 amount of ammonia formed by certain cultures to which may be 

 attributed a small part of the alkaline change in reaction of milk. 

 A third reason to substantiate the belief that the alkaline reaction 

 in milk produced by the alkali-forming bacteria is due to the pro- 

 duction of alkaline carbonates from the salts of organic acids. This 

 will be discussed in detail later. The essential point of the produc- 

 tion of an alkaline reaction during the fermentation of the organic-acid 

 salts and the one upon which the other adjustments of equilibrium 

 depend is the*replacement of the relatively strong organic acids by 

 the relatively weak carbonic acid. 



SOURCES OF THE ALKALI-FORMING BACTERIA. 



The alkali-forming bacteria which are under discussion in this 

 paper were isolated largely from market milk, a few being obtained 

 from the ice cream. Milk, however, can not be considered a source 

 of any bacteria for it is merely a conveyor in which they may grow 

 after being introduced through contamination. While alkali-forming 

 bacteria are commonly found in market milk they must be intro- 

 duced at some stage in its history and must, therefore, have a source. 



Numerous samples of soil were first examined and then plated on 

 extract agar and incubated at 30° C. for 5 days, at which time each 

 colony was picked off and inoculated into litmus-milk tubes. These 

 tubes were incubated at 80° C. for 14 days, after which they were 

 examined for the characteristic reaction produced by bacteria of the 

 alkali group. An alkaline reaction in litmus-milk tubes after 14 

 days' incubation without any sign of peptonization was found to be 

 a practically certain test for the alkali-forming group of bacteria. 



All the samples of soil examined showed the presence of large 

 numbers of alkali-forming bacteria. These organisms were found 

 also in water from shallow and deep wells, springs, and drains. 

 Since they are present in soil it is only natural to expect to find 

 them in water. An examination of the bacteria on the hands of 

 farm laborers showed as high as 12,000,000 of the alkali-forming 

 group of bacteria, this being the approximate number distributed 

 over both hands. The organisms in this case in all probability came 

 from soil. 



Alkali-forming bacteria were not found in the udder and teats of 

 cows in very large numbers, since an examination of 57 samples of 

 milk drawn into sterile tubes from 15 different cows showed their 

 presence in only 10 cases. The highest number found in any case 

 was 30 per cubic centimeter. These organisms were present, how- 

 104410°— 19— Bull. 782 2 



