444 TEXT-BOOK OF PHYSIOLOGY. 



into the lumen of the acinus. During the time these changes are taking 

 place oil-globules make their appearance in the cell protoplasm, some of 

 which are discharged separately into the lumen, while others remain fora 

 time associated with the detached portion of the cell (Fig. 206). 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 from 

 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 secretor activity rather 



than of diffusion and nitration. This is ren- 

 dered probable from the fact that the propor- 

 tions 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 

 FIG. 206. SECTION OF THE suction efforts on the part of the child, aided by 

 MAMMARY GLAND OF A CAT atmospheric pressure and the contractions of 

 r AT Z E riav T Hy E ofaive A o C H * e non-striated muscle-fibers of the lactiferous 



filled with granules and glob- ducts. 



ules of fat. i, 2, 3. Epithe- Influence of the Nerve System. Judging 

 milk " torn analogy, it is probable that the secretion of 

 milk is regulated by impulses emanating from the 

 nerve system, though the exact nerve-channels for the transmission of such 

 impulses have not been determined experimentally. Various attempts 

 have been made to isolate and study these nerves, but the results are incon- 

 clusive. 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 organs of the nerve 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 containing disintegrated epithelial 

 cells and fat-globules, as well as a colostrum corpuscles, which are probably 

 emigrated leukocytes. Colostrum 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. 



THE LIVER. 



The liver is a large gland situated in the upper and right side of the 

 abdominal cavity, where it is held in position largely by ligaments formed by 

 reduplications of the peritoneal investment. In the adult it weighs, freed 

 of blood, from 1300 to 1700 grams. The liver is connected with the duo- 

 denal portion of the intestine by the hepatic duct. It receives blood both 



