820 THE VARIABILITY OF COWS' MILK, i., 



duces. But this influence seems to be nothing more than the 

 general effect of food on the health and activity of a living organ- 

 ism; a well-nourished cow yields more and better milk than a 

 poorly nourished animal. An enormous, amount of work has been 

 done to determine the relation between the food of a cow and its 

 production of milk. The co-operative experiments which have 

 been in progress in Denmark, since 1887, may be referred to as an 

 instance. In these experiments, more than 4,000 cows have been 

 examined, but the results, which have been reviewed by Annett 

 (1915), show that the food has practically no influence on the 

 composition or quantity of fat in the milk produced, as long as the 

 food is sufficient to maintain the cow in vigorous health. These 

 statements refer only to feeding on a commercial scale, and not 

 to the administration of special substances, nor to the eating of 

 plants which may impart distinctive odours or tastes to the milk. 



Much work has also been done to determine the effect of the 

 addition of various inorganic salts to the diet of a cow, but the 

 investigations of von Wendt {loc. cit.), and of Schulte-Bauming- 

 haus (1903), have shown that, in this case, too, no definite effect 

 can be produced on the quality or quantity of the milk secreted. 

 The only effect noticed was a slight increase of calcium in the milk 

 after the administration of calcium salts. The amount of phos- 

 phate could not be correspondingly increased. 



It appears from the work of Graham (1904), however, that the 

 amount of water, which a cow receives with its food, has a definite 

 effect on the yield of milk. A copious water-ration appears to 

 lead to the secretion of a larger volume of more dilute milk. "Milk 

 may be watered through the mouth of the cow." 



The effect of the injection of so-called galactogogues into the 

 circulations of lactating animals may be mentioned here. The 

 most effective and best known of these substances is pituitary 

 extract. It was thought by some investigators that the injection 

 of these substances acted as a stimulus to the secreting cells of the 

 mammary glands, and led to an increased production of milk 

 (Hammond, 1918; Maxwell and Rothera, 1915). The work of 



