THE SECRETION AND PROPERTIES OF MILK 1393 



cells enter into a condition of spontaneous activity. However this may 

 be, there is no doubt that the secretion of the gland, once formed, is 

 continued independently of the foetus, or indeed of any of the pelvic 

 organs. The onset of a new pregnancy brings the secretion to a close. 

 Removal of the ovaries in a cow is sometimes employed as a means of 

 prolonging the secretion of milk. The only condition which is neces- 

 sary for secretion to continue during six to nine months after birth 

 is the repeated emptying of the gland, i.e. the removal of the secreted 

 milk. The process of suckling not only removes the milk already 

 secreted but excites the secretion of more milk. The secretion 

 is certainly subject to nervous influences, but physiologists have 

 not succeeded in either producing secretion by stimulation of the 

 nerves going to the glands, or in stopping secretion by section of these 

 nerves. Moreover the food of the animal may be varied within very 

 wide limits without altering the composition or amount of the milk 

 secreted, provided only that the food is sufficient in amount. The only 

 constituent of the milk for which we have direct evidence of alteration 

 by changes in the food-supply of the mother is the fat. It is well 

 known that the composition of butter may be affected according to the 

 food supplied to the cow. A large supply of oilcake, for instance, may 

 result in the production of a butter which is deficient in the higher fatty 

 acids and is therefore oily at ordinary temperatures. Abnormal fats 

 and fatty acids, such as iodised fats or erucic acid, when administered 

 to an animal in lactation may appear among the fats of the milk. 

 Not only can the secretion and composition of the milk be affected 

 reflexly through the nervous system, as, e.g. under the influence of 

 emotions, but the influence may be reciprocal. This is especially marked 

 in the case of the pelvic organs. The act of suckling excites tonic con- 

 tractions of the uterus. Purring the child to the breast shortly after 

 birth is therefore an important means of causing contraction of the 

 uterus and stopping any tendency to haemorrhage from the venous 

 sinuses opened by the separation of the placenta and foetal membranes. 

 The nursing of her child is therefore an important means of procur- 

 ing a proper involution of the uterus after labour. Many uterine 

 troubles among women may be ascribed to the previous neglect of this 

 elementary duty. 



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