154 ELEMENTARY HISTOLOGY 



B. Glands. 



A gland consists essentially of a layer of epithelial cells 

 secreting some special fluid. The epithelial surface may be flat, 

 but is more usually folded or pitted, often in a very complicated 

 manner, so as to increase the extent of the secreting surface. 



I. Simple Glands. In simple glands the epithelial surface, 

 is increased by simple pit-like depressions, whose mouths serve 

 to discharge the secretion on the free surface. 



Take a prepared section of large intestine of rabbit which has 

 been hardened in chromic add, stained, and cleared in oil of 

 cloves. Mount in balsam, and examine first with the low power, 

 then with the high. Note the following points : 



i. The glands are simple tubular depressions of the 



surface. 



ii. The glandular epithelium lining the pits is a single 

 layer of short columnar granular cells, many of 

 which are swollen to form goblet cells. 



II. Compound Glands. In compound glands each depression 

 instead of being a simple pit is itself subdivided or branched, 

 often in a very complicated manner. There are two chief 

 varieties: (1) tubular glands, in which the several sub- 

 divisions are tubular, and of tolerably uniform diameter 

 throughout : and (2) racemose glands, in which the blind ends 

 of the pits are dilated into globular chambers or alveoli, to 

 which the special glandular epithelium is usually confined. 



a. Compound tubular glands. Take a prepared section of 

 kidney of frog. Examine under a hand lens, and draw on 

 a large scale. Notice that the dorsal surface may be 

 distinguished from the ventral. 



i. The tubular gland cavities are cut at various angles. 

 If cut transversely a tube appears as a circular 

 ring : if cut obliquely, as a more or less elongated 

 elliptical ring : if cut longitudinally, as two 

 parallel rows of epithelial cells. 

 ii. The gland cells form a single layer of cubical granular 



cells, lining the tubes. 



iii. The MalpigMan bodies are spherical dilatations on 

 the tubes, into which project little knots of capillary 



