40 UNIVERSITY OF WISCONSIN STUDIES 



the district nurse system of instructing mothers in uniform 

 and regular feeding of babies suggests that babies respond 

 similarly to like physiological stimuli. In the feeding of calves 

 it is observed that calves like the human infant thrive when 

 fed uniformly upon sweet milk or when fed uniformly upon 

 sour milk but that diarrhea appears promptly when a system 

 of feeding sweet milk is varied by an occasional feeding of 

 sour milk. While frankly admitting the danger of reasoning 

 by analogy, the similarity of the factors observed and of the 

 results obtained in the feeding of calves and of babies strongly 

 suggests that in both cases diarrheal conditions result from 

 sudden changes in the acid reaction of the diet. If this rea- 

 soning is correct, a satisfactory supply of baby milk is char- 

 acterized among other things by a constant acid reaction. 

 Under ordinary conditions the reaction which will be most 

 satisfactory is approximate neutrality. 



If the above explanation of the evil results attending the 

 use of occasional samples of partially sour milk is accepted, it 

 offers an excellent reason for insisting that the public milk 

 suppl}' shall have such a keeping quality as to maintain an 

 essentially unchanged reaction during the time which would 

 ordinarily elapse before its consumption. 



Since the increase in acid reaction of milk is due to the 

 growth of bacteria, the problems of keeping quality are prob- 

 lems of limiting the entrance and activity of germ life and 

 of measuring the activity of the germs which enter. 



The work of Dr. Russell, above referred to, 29 is one of the 

 earliest inquiries as to the source of the bacteria which enter 

 the milk and this type of inquiry has been continued by a 

 number of his students. In connection with this series of 

 studies it has developed that the barn and barn conditions 

 exert surprisingly little influence upon the germ content of 

 milk. While in a few instances the udder flora heavilv 



29 See footnote 25. 



30 H. A. Harding, G. L. Ruehle, J. K. Wilson and G. A. Smith, The Effect 

 of Certain Dairy Operations upon the Germ Content of the Milk, Bulletin 

 365, N. Y. Agr. Exp. Sta., 1913. 



M. J. Prucha and H. M. Weeter, Germ Content of Milk as Influenced 

 by the Factors at the Barn, Bulletin 199, 111. Agr. Exp. Sta., 1917. 



