22 CLEAN MILK 



the cow may act as lactic acid germs and, on entering milk, may 

 cause disease in man drinking it. 



Altogether some ioo varieties of germs may lead to lactic acid 

 fermentation and souring of milk. In general it may be said that 

 when 80 to 90% of the germs in milk belong to the more com- 

 mon type of lactic acid germs the milk is wholesome — even if germs, 

 are in great numbers. If there are less than 20% of lactic acid 

 germs in such milk it should be regarded as unfit food (Conn). 

 Sour milk becomes covered in time by moulds (Oidium lactis) and 

 colored spots produced by various bacteria and fungi. 



At the Paris exposition of 1900 there was an exhibit of dairy 

 products, under care of Major Alford, of the U. S. Department of 

 Agriculture, which consisted of fresh milk and cream shipped from 

 Illinois, New Jersey and New York in hot weather (July). Com- 

 ing some 3,000 to 4,000 miles, the cream and milk were perfectly 

 sweet a fortnight after being bottled, while the only other com- 

 petitor was the French with a local supply which did not keep a. 

 day after reaching the grounds. In the Chicago National Dairy 

 Show in 1906 a sample of cream shipped over 1,000 miles was stilt 

 sweet at the end of 7 weeks. Cleanliness and cold were the only 

 methods used in so wonderfully preserving this milk. 



If milk is very dirty, however, it is not safe to keep it too long 

 with ice, even if it does not sour and is unaltered in taste, as. 

 various sorts of harmful germs may develop at a low temperature. 

 Thus, milk containing, soon after milking, some 800,000 germs to- 

 the cubic centimeter, after four days at 41" F. contained almost five 

 million germs and became sour. At the end of ten days this same 

 milk contained over 400 million germs, or over ten times the num- 

 ber of germs in the same milk kept the same time at 59° F.* The 

 milk kept at a higher temperature soured more quickly and the 

 acid destroyed many of the germs in the process. 



* Swithinbank & Newman. 



