598 THE PHYSIOLOGY OF REPRODUCTION 



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 o.ther cold climates. Unseasonable and inclement weather is 

 believed to have a similar influence. 1 



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 metabolism may .so change the character of the 

 secretion in women as to make it no longer fit for the child. 

 Violent emotion or shock have been known to lead to the complete 

 suppression of the mammary secretion. 2 The employment of certain 

 drugs also influences it. Thus atropine, if given in sufficient 

 quantities, stops the secretion altogether, or if supplied in smaller 

 amounts causes the milk to become more concentrated. 



The occurrence of menstruation in women, or of heat in certain 

 animals, may have a deleterious infhience upon the milk, and so 

 upon the offspring (see p. 362). In the case of cows, oastrus generally 

 has a marked effect on the milk-yield, which as a rule shows at first 

 a perceptible diminution, followed usually at the next milking by a 

 yield well above the average. The fat content is generally at first 

 considerably reduced, but at the following milking is sometimes 

 abnormally high, or may be still abnormally low. On the two or 

 three days preceding the outward manifestations of heat, the fat 

 content tends to be decided!}' above the average. 



Ovariotomy is stated to have a beneficial effect upon goat's milk, 

 relieving it of the characteristic hircine odour, increasing the quantity 

 of butter, casein, and phosphoric acid (though decreasing the lactose 

 present), and producing a greater and more long-continued secretion. 3 

 The removal of the ovaries in cows may also tend to improve the 

 quality of the milk, rendering it richer than when the animals have 

 been some months pregnant. 4 



The advance of lactation may be accompanied by changes both 

 in the amount and in the composition of the mammary secretion, 

 but the changes vary greatly in different individuals. In cows, the 

 milk fat secreted in the first few days after parturition is poor in 



1 Crowther, lor. ,-,'t. 

 - Williams, loc. cit. 



3 Oceanu and Babes, " Les Effets Physiologiques de TOvariotomie," C. Jl. <><> 

 I'Acad. dex Sciences, vol. cxl., 1905. 



4 Wallace, loc. cit. 



