THE SECRETION AND PROPERTIES OF MILK 1245 

 source of the inhibitory stimulus is removed and the overgrown gland-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 inde- 

 pendently 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 necessary 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 contractions of the uterus. Putting the child to the 

 breast shortly after birth is therefore an important means of causing con- 

 traction of the uterus and stopping any tendency to haemorrhage from the 

 venous sinuses opened by the separation of the placenta and foetal mem- 

 branes. The nursing of the child is therefore an important means of pro- 

 curing a proper involution of the uterus after labour. Many uterine troubles 

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

 duty. 



