402 TEXT-BOOK OF PHYSIOLOGY. 



protoplasm, some of which are discharged separately into the lumen, 

 while others remain for a time associated with the detached portion of 

 the cell (Fig. 183). From these histologic changes it is inferred that 

 the caseinogen and fat are products of the metabolism of the cell 

 protoplasm and not derived directly through the lymph from the blood. 

 The lactose apparently has a similar origin, as appears from the fact 

 that it is not found either in the blood or any other tissue, and that it 

 is formed independently of carbohydrate food. The water, and 

 especially the inorganic salts, are the result of secretory activity rather 

 than of diffusion and filtration. This is rendered probable from the 

 fact that the proportions of the inorganic salts of milk are more closely 

 allied to those of the tissues of the new-born child than to blood. 

 With the passage of the water and salts into the lumen of the acinus 



the proteids undergo disintegration and 

 solution and the liquid assumes the 

 characteristics of milk. 



The discharge of milk is occasioned 

 by the suction efforts on the part of the 

 child, aided by atmospheric pressure and 

 the contractions of the non-striated mus- 

 cle-fibers of the lactiferous ducts. 



Influence of the Nerve System. 

 Judging from analogy, it is probable 

 FIG. 183. SECTION OF THE that . the secretion of milk is regulated 

 MAMMARY GLAND OF A by influences emanating from the nerve 

 S C T A /G E s IN op TH L E A cxf T r N Y fstem, though the exact nerve-channels 

 A. Cavity of alveoli filled ior tne transmission of such influences 

 with granules and globules have not been determined experimentally. 



Ln at in vario 2 us 3 s tag P e fof Various attempts have been made to 



milk-formation. ( Yeo.} isolate and study these nerves, but the 



results are inconclusive. It is well known 



that emotional states on the part of the mother modify the quantity 

 as well as quality of milk, indicating a connection between the gland- 

 cells and the central nervous system. Nerve terminals have been 

 discovered in and around the epithelial cells a fact which supports 

 this view. 



Colostrum. Within a day or two after parturition the alveoli 

 become filled with a fluid which in some respects resembles milk 

 and which has been termed colostrum. This is a watery fluid con- 

 taining dismtegrated epithelial cells, fat-globules, as" w"ell as colos- 

 im corpuscles, which are probably emigrated leukocytes. Colos- 

 trum is distinguished from milk in being richer in sugar and inorganic 

 salts. It is said to possess constituents which act as a laxative to 

 the young child, s 



