COMPOUND ALIMENTARY SUBSTANCES. 79 



and to some persons is agreeable. Its specific gravity is 

 . about 1,030, though this is subject to considerable variations. 

 The proportion of cream in milk of good quality is from ten 

 to fifteen parts per hundred by volume. Ordinary milk 

 hardly contains so much. Milk that contains more than 

 fifteen per cent, of cream may be regarded as excessively 

 rich. These indications may be easily obtained by allowing 

 milk to stand for twenty-four hours in a graduated glass 

 tube. These little instruments, called lactometers, are fre- 

 quently used for testing the milk of wet-nurses. It has been 

 found that the proportion of fatty matter in cows' milk is 

 much greater toward the end of a milking than at first. In 

 an observation by Quevenne, during the first part of the milk- 

 ing the proportion of cream was five per cent., during the 

 middle period fifteen per cent., and during the last period 

 twenty-one per cent. 1 



The diet of the animal has an important influence on the 

 quality of the milk and butter. Almost every one is famil- 

 iar with the peculiarly disagreeable flavor of these articles 

 when the cows have had access to leeks or onions. Except 

 when animals are fed in pastures of great richness, the best 

 milk is obtained by feeding judiciously in the stable, taking 

 care to give water at proper intervals, to clean the animals 

 carefully, and to allow sufficient exercise, with opportunities 

 for rubbing the hide, etc. 



Cream, though of less specific gravity than milk, under 

 certain conditions is much more nutritious. Added to other 

 articles of food, it frequently corrects defective nutrition more 

 effectually than cod-liver oil, or any article that may be ex- 

 hibited for that end. It contains a large quantity of fat, and 

 has a very delicate and delicious flavor. 



Buttermilk, the residue in the manufacture of butter, 

 contains all the constituents of milk except the fatty mat- 

 ters, and is frequently used as an article of diet, particularly 



1 In PATEN, op. cit., p. 145. 



