68 HUMAN PHYSIOLOGY. 



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

 mation 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, albumen, 

 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 

 thymus 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 

 trabeculae are given off, which penetrate the substance of the gland, form- 

 ing 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 

 semi-fluid substance composed of numerous small cells resembling lymph 

 corpuscles. The spleen pulp is a dark red, semi-fluid substance, of a soft 

 consistence, contained in the meshes of the trabeculae. In it are found 

 numerous corpuscles, like those observed in the Malpighian bodies, blood 

 corpuscles in a natural and altered condition, nuclei and pigment granules. 



Function of the Spleen. Probably influences the preparation of the 

 albuminous food for nutrition ; during digestion the spleen becomes larger, 

 its contents are increased in amount, and after digestion it gradually dimin- 

 ishes in size, returning to the normal condition. 



