Chap, xvii.] OF SECRETION AND EXCRETION IN GENERAL. 259 



plasmas ; they fabricate, at the expense of the blood, special 

 products, which pass afterwards into the circulation by osmosis. 

 Eut essentially closed glands and glands with canals are very 

 analogous. In both the secreting elements are cells, anatomically 

 comparable with the epithelial cells covering the mucous mem- 

 branes and the skin. The mode of action of these cells has, 

 moreover, nothing exceptional. Every anatomical element is a 

 living laboratory, borrowing by election from the nutritive liquids 

 materials which it fashions and traaisforms. This is what the 

 glandular epithelial cells do (Fig. 35) ; but as in them the vege- 

 tative properties are very energetic, they transform with a greater 

 activity. The special substance, as soon as elaborated, is expulsed 

 from the secreting cell either by simple osmosis or set at liberty 



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Fig. 35. 

 Human gastric gland, with acid secretion, as example of simple gland. 



by rupture or resorption of the cellular wall. In the dosed 

 glands the product of the secretion traverses the wall of the 

 capillaries, which are in contact with the secreting cells, and is 

 afterwards conveyed into the circulation. This is what takes 

 place, for instance, with the glycogenical cells of the liver, which 

 we have already mentioned. The cells elaborate the materials 

 which the blood of the intestine brings them, and restore to the 

 fine capillaries in contact with them those same materials 

 metamorphosed into sugar, which serves for the general nuti'ition. 

 But if the glycogenical function of the liver is now well eluci- 

 dated, this is far from being the case with many other closed 

 glands. It would be needful to make for each of those glands 



s 2 



