80 



SECRETION. 



FIG. 4. 



important bearing upon the mechanism of the secretion of 



milk. 



During the intervals of lactation, as the lactiferous ducts 



become retracted, the glandular culs-de-sac disappear ; and 



in pregnancy, as the gland takes on its full development, the 



ducts branch and extend 

 themselves, and the vesi- 

 cles are gradually devel- 

 oped around their ter- 

 minal extremities. These 

 changes in the develop- 

 ment of the mammae at 

 different periods are most 

 remarkable, and are not 

 observed in any other part 

 of the glandular system. 1 



Mechanism of the Se- 

 cretion of Milk. With the 

 exception of water and in- 

 organic principles, all the 



Ducts and acini of the mammary piand. (LiT- important and character- 



TRfi ET ROBIN. Dictionnaire de medecine, i^l-ir* nrmefi-H-ionfe rf -flm 



Paris, 1865, Article, Mamdle.) m, nipple; lstic Constituents Ol 



, larger ducts ; r, small duct ; , acini. milk &TQ formed ill the 



substance of the mam- 

 mary glands. The secreting structures have the property 

 of separating from the blood a great variety of inorganic 

 principles ; and we shall see, when we come to study the 

 composition of the milk more minutely, that it furnishes 



1 Sir Astley Cooper, in his admirable monograph upon the anatomy and 

 diseases of the breast, published in 1840, was the first to give any clear idea 

 of the minute structure of the mammary glands. His observations, however, 

 have been much extended by later anatomists. The paper on the breast has 

 been republished in this country. COOPER, The Anatomy and Diseases of the 

 Breast, with numerous plates. To which are added his various Surgical Papers, 

 now first published in a collected form, Philadelphia, 1845. 



