74 HUMAN PHYSIOLOGY. 



Influences modifying the secretion. During lactation there is a 

 demand for an increased amount of fluid, and if not supplied, the amount 

 of milk secreted is diminished. Good food in sufficient quantity is neces- 

 sary for the proper elaboration of milk, though no particular article influ- 

 ences its production. 



Mental emotion at times influences the character of the milk, decreasing 

 the amount of its different constituents. 



Mechanism of Secretion. The water and salts preexist in the blood 

 and pass into the gland vesicles by osmosis. The casein, fatty matter and 

 sugar appear only in the mammary gland, but the mechanism of their 

 formation is not understood. 



Colostrum is a yellowish, opaque fluid, formed in the mammary glands 

 toward the latter period of utero-gestation ; it consists of water, albumin, 

 fat, sugar and salts, and acts as a laxative to the newly-born infant. 



VASCULAR OR DUCTLESS GLANDS. 



The Vascular Glands are regarded as possessing the power of acting 

 upon certain elements of the food and aiding the process of sanguinifica- 

 tion; of modifying the composition of the blood as it flows through their 

 substance, by some act of secretion. 



The vascular glands are the spleen, supra-renal capsules, thyroid and 

 thymiis glands. 



The Spleen is about 5 inches in length, 6 ounces in weight, of a dark 

 bluish color, and situated in the left hypochondriac region. It is covered 

 externally by a reflection of the peritoneum, beneath which is the proper 

 fibrous coat, composed of areolar and elastic tissue and non-striated muscu- 

 lar fibres. From the inner surface of the fibrous envelope processes or tra- 

 beculae are given off, which penetrate the substance of the gland, forming a 

 network, in the meshes of which is contained the spleen pulp. The splenic 

 artery divides into a number of branches, some of which, when they become 

 very minute, pass directly into veins, while others terminate in true capillaries. 



As the capillary vessels ramify through the substance of the gland, their 

 walls frequently disappear and the blood passes from the arteries into the 

 veins through lacuna (Gray). 



The splenic or Malpighian corpuscles are small bodies, spherical or 

 ovoid in shape, the -fa of an inch in diameter, situated upon the sheaths of 

 the small arteries. They consist of a delicate membrane, containing a 



