566 THE PHYSIOLOGY OF REPRODUCTION 



with them.^ It is stated also that certain particular foodstuffs 

 have a very appreciable effect upon the quantity and quahty 

 of milk in cows. Thus bean-meal is said to increase the flow of 

 really good milk, unless it is given in immoderate quantities. 

 Brewers' and distillers' grains are hkewise described as having 

 a beneficial influence upon the milk supply, but if given too 

 freely they tend to injure the breeding capacity, and in conse- 

 quence are most used in town dairies where the cows are 

 not bred from.^ Many substances ingested by the mother pass 

 unaltered into the milk. It is well known that certain foods 

 {e.g. turnips) cause an unpleasant taste or smell in the milk of 

 cows to which they are suppUed. Lehmann's experiment, in 

 which sodium sulphindigotate was injected into the veins of a 

 goat, and shortly afterwards made its appearance in the milk, 

 has been already referred to (p. 558). So also it has been found 

 that immunity from disease may be acquired by young animals 

 being suckled by a female which had previously become immune, 

 the antibody to the disease being absorbed in the ingested miUc. 



It is generally recognised that the nature of the surroundings 

 has an influence over the mammary secretion. For example, 

 the composition of the fat in the milk of cows varies with the 

 condition of the animals. Circumstances tending to cause 

 discomfort usually lower the proportion of volatile acids present 

 in the butter-fat, but the variation in the composition is very 

 irregular, and appears to depend partly upon the nervous 

 temperament of the cow. Extremes of heat and cold are said 

 to produce a decrease in the percentage of volatile acids, a fact 

 which has been put forward as an explanation of the general 

 poorness in these compounds of butters from Siberia and 

 other cold chmates. Unseasonable and inclement weather is 

 beheved to have a similar influence.^ 



In women exercise in the open air may not infrequently 

 increase the flow of milk. Nervous and mental influences or 

 any cause which affects the general metabohsm may so change the 

 character of the secretion in women as to make it no longer fit 



> Williams, Obstetrics, London, 1904. 



■■= Wallace (R.), Farm Live Stock of Great Britain, ith Edition, Edinburgh, 

 1907. 



' Crowther, loc, cit. 



