324 



HAND-BOOK OF PHYSIOLOGY. 



the large glands converge and unite to form larger and larger branches, 

 and at length by one common trunk, open on a free surface of membrane. 

 Among these varieties of structure, all the secreting glands are alike in 

 some essential points, besides those which they have in common with all 

 truly secreting structures. They agree in presenting a large extent of 

 secreting surface within a comparatively small space; in the circumstance 



FIG. 220. Plans of extension of secreting membrane by inversion or recession in form of cavities. 

 A, simple glands, viz. g, straight tube; h, sac; i, coiled tube. B, multilocular crypts; fc, of tubular 

 form: I, saccular. C, racemose, or saccular compound gland ; m, entire gland, showing branched 

 duct and lobular structure: n, a lobule, detached with o, branch of duct proceeding from it. D, com- 

 pound tubular gland. (Sharpey.) 



that Avhile one end of the gland-duct opens on a free surface, the opposite 

 end is always closed, having no direct communication with blood-vessels, 

 or any other canal; and in a uniform arrangement of capillary blood- 

 vessels, ramifying and forming a network around the walls and in the 

 interstices of the ducts and acini. 



Process of Secretion. In secretion two distinct processes are con- 

 cerned which may be spoken of as, 1. Physical, and 2. Chemical. 



