EXTERNAL SECRETIONS 487 



from the nerve system, though the exact nerve-channels for the trans- 

 mission of such impulses have not been determined experimentally. 

 The results of experiments made on the nerve distribution to the 

 mammary gland of the goat are unsatisfactory and contradictory and 

 do not shed much light on the subject. Even after division of all nerves 

 to this gland in this animal, secretion continues in an apparently normal 

 manner. Nevertheless, it is well known that emotional states on the part of 

 the mother modify the quantity as well as quality of milk, indicating a con- 

 nection 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 

 leukocytes containing fine fat-globules. Colostrum is distinguished from 

 milk in being richer in sugar and inorganic salts. It also differs from milk 

 in undergoing coagulation by heat which is supposed to be due to the pres- 

 ence of a globulin. Its coagulation point is about J2C. 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 

 from the hepatic artery and from the portal vein, and in this respect differs 

 from all other glands in the body. The epithelial structures of the liver are 

 inclosed by a firm fibrous membrane, known as Glisson's capsule. At the 

 transverse fissure it invests and follows the blood-vessels, which there enter, 

 in all their ramifications through the gland. 



Structure of the Liver. The liver is composed of an enormous num- 

 ber of small masses, rounded, ovoid, or polygonal in shape, called lobules, 

 measuring about one millimeter in diameter and separated from one another 

 by a narrow space in which are to be found blood-vessels, lymphatics, and 

 hepatic ducts, supported by connective tissue. In the pig this space and its 

 contained elements is quite distinct, sharply marking out the border of 

 the lobule (Fig. 215). This is not so apparent in man. Each lobule is 

 made up of irregular or polygonal-shaped cells measuring about 30 to 40 

 micromillimeters in diameter. These cells are arranged in a radial manner 

 from the center to the circumference of the lobule (Fig. 216). Each cell 

 possesses one and at times two^nuclei. There is no evidence for the exist- 

 ence of a distinct cell-wall. The cell protoplasm frequently contains glob- 

 ules of fat, granules of a protein nature, granules of glycogen, pigment ma- 

 terial, etc. The appearance presented by the cell will vary considerably, ac- 

 cording to the time it is observed. Thus there may be a complete absence of 

 these constituents, when the cell may present a series of vacuoles separated 

 by bands of protoplasm. The cells are the secreting structures of the liver, 



