GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 253 



flat surfaces which secrete the serous fluids. Nearly all the 

 other glands, however, are modified. Usually space is saved 

 by pitting in the secreting surface and thus tubular glands 

 arise. Sometimes these, instead of being straight and 

 tubular, become rounded and sac-like, in which case such 

 a gland is called a racemose gland. When several such 

 tubular or racemose glands have a common duct leading 

 from them, the entire structure is spoken of as a compound 

 gland. . 



Illustrations of the simple tubular glands may be found 

 in the gastric glands of the stomach, and in the crypts of 

 Ljeberkiihn. Illustrations of the simple racemose glands 

 occur in the sebaceous or oily glands of the skin. How- 

 ever, most of the larger glands, such as the pancreas and 

 the salivary glands, are of the compound racemose kind. 

 Such a compound racemose gland might be compared to a 



Fig. 98. SECTION OF A RACEMOSE GLAND, SHOWING THE COMMENCEMENT OF A DUCT 



IN THE SECRETING ALVEOLI. (After Shafet.) 



a, an alveolus; 6, basement membrane lining the duct d'; c, connective tissue be- 

 tween the alveoli; d, duct; s, semilunar reserve cells. 



very full bunch of grapes in which the central stalk figures 

 as the single duct, while the individual grapes represent the 

 ultimate sac-like expansions, in which the process of secre- 



