SECRETION OF MILK. 331 



of blood than at other times. Pregnancy favors the development of the 

 secreting portions of the glands but does not induce secretion. On the other 

 hand, when pregnancy occurs during lactation, it diminishes and modifies, 

 and it may arrest the secretion of milk. The secreting action of the mam- 

 mary glands is nearly continuous. When the secretion of milk has become 

 fully established, while there may be certain times when it is formed in 

 greater quantity than at others, there is no actual intermission in its pro- 

 duction. 



General Conditions which modify the Lacteal Secretion. Very little is 

 known concerning the physiological conditions which modify the secretion 

 of milk. When lactation is fully established, the quantity and quality of the 

 milk secreted become adapted to the requirements of the child at different 

 periods of its existence. In studying the composition of the milk, therefore, 

 it will be found to vary considerably in the different stages of lactation. 

 It is evident that as the development of the child advances, a constant in- 

 crease of nourishment is demanded ; and as a rule, the mother is capable of 

 supplying all the nutritive requirements of the infant for eight to twenty 

 months. 



During the time when such an amount of nutritive matter is furnished 

 to the child, the quantity of food taken by the mother is sensibly increased ; 

 but observations have shown that the secretion of milk is not much influ- 

 enced by the character of the food. It is necessary that the mother should be 

 supplied with good, nutritious articles ; but as far as solid food is concerned, 

 there seems to be no great difference between a coarse and a delicate ali- 

 mentation, and the milk of females in the lower walks of life, when the gen- 

 eral condition is normal, is fully as good as in women who are able to live 

 luxuriously. It is, indeed, a fact generally recognized by physiologists, that 

 the secretion of milk is little influenced by any special diet, provided the ali- 

 mentation be sufficient and of the quality ordinarily required by the system 

 and that it contain none of the few articles of food which are known to have 

 a special influence upon lactation. It is very common, however, for women 

 to become quite fat during lactation ; which shows that the fatty cbnstituents 

 of the food do not pass exclusively into the milk, but that there is a tendency, 

 at the same time, to a deposition of adipose tissue in the situations in which 

 it is ordinarily found. It is a matter of common experience, that certain 

 articles, such as acids and fermentable substances, often disturb the digestive 

 organs of the child without producing any change in the milk, that can be 

 recognized by chemical analysis. The individual differences in women, in 

 this regard, are very great. 



The statements with regard to solid food do not apply to liquids. Dur- 

 ing lactation there is always an increased demand for water and for liq- 

 uids generally; and if these be not supplied in sufficient quantity, the 

 secretion of milk is diminished and its quality is almost always impaired. 

 It is a curious fact, which has been fully established by observations upon 

 the human subject and the inferior animals, that while the quantity of milk 

 is increased by taking a large amount of simple water, the solid constituents 



