CHAPTER XXXI. 

 MILK BACTERIOLOGY. 



ABOUT ten billion gallons of milk are produced annually in the 

 United States, one-fourth of which is consumed as milk and the 

 other three-fourths as butter and cheese. The quantity of milk 

 consumed varies in different localities, being greater in the North 

 than in the South and greater in the country districts than in the 

 city. It also varies with different classes, as seen from a survey made 

 by Williams of fifteen sections of Rochester, New York. He found 

 that the average consumption of milk by 21,600 individuals was 

 little more than 0.24 pint per capita. Furthermore, he found that 

 the poor not only used less milk and bought it in smaller quantities 

 than the well-to-do, but the use of store milk and of condensed milk 

 was largely confined to the laboring classes. In other words, the 

 people who most needed to be careful in their buying used smaller 

 quantities of the cheapest food which they bought in the most 

 expensive manner. It is usually stated that about 16 per cent, of 

 the average dietary in the United States consists of milk and milk 

 products, yet the average daily consumption per capita of milk as 

 such is only 0.6 pint, which is about half what it should be. 



Milk as Food. Milk has been regarded from the earliest times as a 

 most important article of food, and although little was known as to 

 its chemical composition previous to the eighteenth century, the 

 ancients attributed many and peculiar hidden virtues to it. 



Good whole milk or skimmed milk are among the best and cheap- 

 est of foods. Good fresh milk is all but essential to the welfare of 

 young children, and to the babe that for any reason is deprived 

 of its mother's milk, cows' milk is practically indispensable. The 

 reason is due to its composition. The composition of human and 

 cow's milk is as follows : 



Fat, Lactose, Protein, Ash, 



per cent. per cent. per cent. per cent. 



Human milk .... 2-4 6.0-7.5 0.7-1.5 0.15-0.30 



Cows' milk .... 3-6 3.5-5.0 2.5-4.0 0.66-0.77 



Besides these substances both cows' and mothers' milk carry 

 organic substances which contain little or no nitrogen, one of which 

 is soluble in ether and alcohol, the other in water. The true chemical 

 nature of these is unknown. The amount of these substances in 

 human milk at the beginning of lactation is about 1 per cent.; in 



