326 THE DUCTLESS GLANDS. 



pelled 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 ap- 

 pears, however, to be a modification of the process of secre- 

 tion, 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 previously discharged from the 

 secreting organ, or made use of for any secondary 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 thymus and thyroid glands, 

 the supra-renal capsules, and, according to (Esterlin and Ecker 

 and Gull, the pineal gland and pituitary body ; possibly, also 

 the tonsils. 



The solitary and agminate glands of the intestine (p. 242), 

 and lymph-glands in.general, also closely resemble them ; in- 

 deed, both in structure and function, the vascular glands bear 

 a close relation, on the one hand, to the true secreting 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 



FIG. 106. 



Vesicles from the thyroid gland of a child (from Kolliker) 25. o _ a, connective tissue 

 between the vesicles ; b, capsule of the vesicles ; c, their epithelial lining. 



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. They are mainly composed of vesicles, or sacculi, either 

 simple and closed, as in the thyroid (Fig. 106), and supra- 



