SECRETING GLANDS 189 



Finally the period of secretory activity arrives, and the se- 

 cretion is poured into the glandular lumen; the cells become 

 shrunken and the lumen of the tubule correspondingly dilated. 

 The cytoplasm returns to its former condition; if the secre- 

 tion is of a granular character the cell becomes clearer, but 

 if watery the cytoplasm acquires a finely granular appearance. 

 The nucleus resumes its former central location and the cell 

 enters upon a second period of constructive and accumulative 

 activity. 



Many of the serous secreting cells contain minute intracellular 

 canals which connect with a network of intercellular passages about 

 the cell. The intercellular canaliculi may, on the one hand, open 

 into the glandular lumen, or they may communicate with the 

 tissue spaces of the tunica propria. This system of intracellular 

 and intercellular canaliculi may thus serve either as a system of 

 nutrient channels or as a network of secretory capillaries by which 

 the secretion is conveyed from the interior of the secreting cells 

 to the lumen of the gland or even to the duct system. Nutrient 

 and secretory canaliculi of this nature have been demonstrated in 

 the secreting cells of the liver, cardiac glands of the stomach, sali- 

 vary glands, pancreas, adrenal, and epididymis, but they are not 

 by any means confined to the actively secreting cells, for they 

 have been found in the cells of bladder epithelium (Holmgren) 

 and are highly developed in the nerve cells (Holmgren, Golgi, 

 et als.). 



Simple tubular glands occur in the mucous membrane of the 

 small and large intestine as the crypts of Lieberkiihn. In shape 

 these glands resemble a test-tube. They form straight tubules 

 which open on the free surface of the membrane, are of approxi- 

 mately equal caliber throughout, and at their deeper end terminate 

 in a blind extremity. The tubules are lined with epithelium and 

 are embedded in a thin vascular tunica propria. Their epithelium 

 includes the usual columnar and goblet cell types, the latter being 

 more abundant near the mouth of the gland. Near the blind ex- 

 tremity are certain granular cells, the granules of some of which 

 are slightly basophilic : other cells possess coarse granules which 

 are highly acidophile, as demonstrated by Kultschitsky* in the 

 intestinal glands of the dog, an observation which is easily cor- 

 roborated for the simple tubular glands in the small intestine of 



man. 



* Arch. f. inik. Anat,, 1897. 



