618 THE SECRETION OF MILK. [Book ii. 



of the formation, by the metabolic activity of the secreting cell, 

 of the representatives of the three great classes of food-stuffs, 

 proteids, fats, and carbohydrates. 



§ 412. That both the secretion and ejection of milk are 

 under the control of the nervous system is shewn by common 

 experience, but the exact nervous mechanism has not yet been 

 fully worked out. While erection of the nipple ceases when 

 the spinal nerves which supply the breast are divided, the secre- 

 tion continues, and is not arrested even when the sympathetic 

 as well as the spinal nerves are cut. 



