370 MILK BACTERIOLOGY 



functions and furnishes essential constituents to the growing animal 

 which is not furnished by many other foods and which cannot be 

 measured in heat units. It contains "vitamins" or "accessories," 

 substances belonging to a group of agents which are widely dis- 

 tributed in nature and which are now regarded as essential factors 

 in diet. 



Hopkins clearly demonstrated that the feeding of very small 

 quantities of milk to rats which had been living on a diet inadequate 

 for normal growth brought about a rapid growth in the animals. 

 Moreover, Osborne and Mendel in their extensive experiments on 

 the growth of animals have for several years been employing 

 "protein-free milk" as an indispensable ingredient of their basic 

 diet to which certain isolated food substances are added. They find 

 that no artificial imitation of this natural mixture has been devised 

 to replace it satisfactorily for considerable periods of time. The 

 weight and health of adult rats can be maintained for many months 

 on a ration consisting of protein, starch, sugar, protein-free milk, 

 and lard. Young animals kept on this mixture decline after a time. 

 If, however, butter is substituted for the lard growth is resumed. 

 The active constituent is the fat soluble vitamin of the butter in 

 contrast to the water soluble accessories present in the protein-free 

 milk. Ordinary skimmed milk contains both the fat-soluble and 

 water-soluble accessories. The influence of milk and sour milk upon 

 the growth of chicks is seen from the following summary of a 

 great many tests made by Rettger: 



Gain per chick, Pounds. 



Fed sour milk 0.48 



Fed sweet milk 0.44 



Given no milk . 39 



Moreover, individuals who have lived to extreme old age have 

 used milk in some of its forms. Several French laborers whose diet 

 consisted largely of milk lived to be one hundred and ten years or 

 over. There are also authentic records of a number of individuals 

 in the Balkans, Persia, Arabia, and in the Caucasus Mountains who 

 have reached extreme old age, whose main diet was milk. 



Scientists have long studied the habits of these centenarians and 

 their diet was found to contain large quantities of sour milk. Metch- 

 nikoff attributes their long life as due to specific bacteria taken into 

 the alimentary tract with the sour milk, and the organism, Bacillus 

 bulgaricus, is sometimes known as "the bacillus of long life" and is 

 often used by the physician in combating certain digestive disturb- 

 ancessometimes with good effects and at other times without. 

 The cause of these failures is only at the present time being fully 

 understood. 



Even the acid-forming bacteria cannot gain the ascendency when 

 growing on a protein-rich diet, but if grown on a carbohydrate diet 



