HAND-BOOK OF PHYSIOLOGY. 



CHAPTER XIV. 



THE VASCULAR GLANDS. 



THE materials separated from the blood by the ordinary process of 

 secretion in glands, are always discharged from the organ in which they 

 are formed, and are either straightway expelled from the body, or if they 

 are again received into the blood, it is only after they have been altered 

 from their original condition, as in the cases of the saliva and bile. There 

 appears, however, to be a modification of the process of secretion, in which 

 certain materials are abstracted from the blood, undergo some change, 

 and are added to the lymph or restored to the blood, without being pre- 

 viously discharged from the secreting organ, or made use of for any second- 

 ary purpose. The bodies in which this modified form of secretion takes 

 place, are usually described as vascular glands, or glands without ducts, and 

 include the spleen, the tliymus and thyroid glands, the supra-renal cap- 

 sules, the pineal gland and pituitary body, the tonsils. The solitary and 

 agminate glands (Peyer's) of the intestine, and lymph-glands in general, 

 also closely resemble them; indeed, both in structure and function, the 

 vascular glands bear a close relation, on the one hand, to the true secret- 

 ing glands, and on the other, to the lymphatic glands. The evidence in 

 favor of the view that these organs exercise a function analogous to that of 

 secreting glands, has been chiefly obtained from investigations into their 

 structure, which have shown that most of the glands without ducts contain 

 the same essential structures as the secreting glands, except the ducts. 



THE SPLEEN. 



The Spleen is the largest of the so-called ductless glands; it is situated 

 to the left of the stomach, between it and the diaphragm. It is of a deep 

 red color, of a variable shape, generally oval, somewhat concavo-convex. 

 Vessels enter and leave the spleen at the inner side (hilus). 

 VOL. II. l. 



