50 MILK AND THE PUBLIC HEALTH CHAP 



more than a hundred million organisms per c.c. after five to six 

 weeks. She showed that there were present both acid-forming 

 and protein-decomposing bacteria. The casein was digested 

 until rather more than 50 per cent of it was destroyed and 

 changed into soluble compounds (caseoses, arnino acids, etc.). 



Kavenel, Hastings, and Hammer 1 also investigated this 

 subject. They found that in samples of milk kept at C. 

 there was a slowly developed but marked increase in the 

 bacterial content, resulting in an increase of acidity, an 

 increase in the percentage of soluble nitrogen (so that it 

 eventually amounted to over 70 per cent of the total nitrogen), 

 and a decrease in the total nitrogen-content probably due 

 to a liberation of free nitrogen. The kind of increase they 

 met with is shown in the following table : 



Bacterial Content of Specimens kept at C. 



The Barn milk was a very pure milk from the University Herd, and con- 

 taining only about 3000 bacteria per c.c. The Dairy milk was an average dairy 

 milk. The plating medium was lactose agar, and the plates were incubated at 

 37 C. 



While these results are interesting, the broad practical 

 conclusion remains, that if milk is kept at C. or even at 

 10 C. (see Conn and Esten below) no material alteration of 

 the germ-content takes place for at least several days. 



Of interest and practical importance greater than the total 

 bacterial multiplication in milk, is the relative growth of the 

 different varieties of bacteria under different conditions. In 

 this connection, Conn and Esten 2 have published a valuable 

 report upon " The effect of different temperatures in de- 



1 Journal of Infect. Diseases, 1910, vol. vii. p. 38. 

 2 Sixteenth Annual Report, Storrs Agric. Experiment Station, 1904, p. 27. 



