LACTATION 565 



That the yield and composition of the milk varies in the 

 different breeds is generally admitted. Thus Jersey cows yield 

 a larger proportion of butter fat than Ayrshires. But of all the 

 factors enumerated above, diet is perhaps the most important. 

 The richest and al;o the most abundant supply of milk is usually 

 yielded when the food supply is liberal. As a result of giving 

 food rich in protein substances, the milk supply tends to contain a 

 larger quantity of protein, sugar, and fat (especially the latter). 

 Schafer has pointed out, however, that because an excess of a 

 particular organic principle in the food causes an increase of 

 certain constituents in the milk, it must not be supposed that 

 these constituents are necessarily formed directly from such 

 material, " for the effect may be produced indirectly by the 

 functions of the gland-cells becoming modified, according to the 

 nature of the pabulum they are receiving. Looked at in this 

 hght, certain substances may be said to stimulate the cells of 

 the glands to increased activity in all directions, tending to the 

 production of a larger quantity of milk rich in all lands of sol d 

 constituents ; whilst other substances may be looked upon as 

 stimulating the cells in a special manner, tending to the increased 

 production of certain only of the constituents of the milk." ^ 



According to Crowther's researches on cows, change from a 

 highly nitrogenous diet to one relatively poor in nitrogen causes 

 secretion of a greater quantity of milk, but there is a decrease 

 in the fat content, this being more pronounced in the morning 

 than in the evening milk. A change in the reverse direction 

 effected an improvement in the quaUty of the milk. Concen- 

 trated food given either in the morning or evening tended to 

 increase the fat content of the morning milk, but had httle or 

 no effect upon the evening milk. These alterations were found 

 to persist without appreciable diminution for fuUy five weeks 

 after the change of treatment. 



There are a number of preparations in the market, known as 

 galactagogues, which are said to increase the flow of milk in 

 women, but, according to WiUiams, any virtue which they 

 possess is due largely to the quantity of fluid which is taken 

 1 Schafer, loc. cit. There is evidence also that an abnormal diet during 

 and previous to pregnancy may arrest the normal mammary development. 

 See Watson (B. P.), "The Effect of a Meat Diet on Fertility and Lactation," 

 Proc. Boy. Soc. Edm., vol. xxvii., 1907. 



