60 



NORMAL HISTOLOGY. 

 FIG. 46. FIG. 47. 



Diagrams representing various types of gland. 



Fig. 46. Racemose saccular gland: /,/, ducts; g, acinus. 



Fig. 47. Compound tubular gland, with a marked distinction in the character of the epi- 

 thelium in the duct and acini : c, duct epithelium ; /, duct ; d, lumen of the acinus ; 

 e, secreting epithelium. This type of gland is common. This figure is introduced to show 

 how difficult it might be to detect the lumen of the acinus in sections of such a gland. 

 The lumen is of very small diameter (its size is exaggerated in this diagram) and runs 

 such a tortuous course among the epithelial cells that even perfect cross-sections of the 

 acinus might fail to reveal it if it happened at that point to run obliquely to the axis 

 of the acinus. It would then appear merely as a small clear spot upon the granular 

 cytoplasm of the cell that lay immediately beneath it. s, s', represent the way in which 

 two such sections would contain portions of the acinus. The lumen in s' would be more 

 easily detected than in s, because its general direction is more rectilinear and more 

 nearly coincident with the line of vision. 



It is rarely possible to trace the connection between the ducts 

 and other portions of a gland in sections, for the axes of these dif- 

 ferent parts seldom lie in one plane. As a result of this circum- 

 stance, sections of glands usually present a collection of round or 

 oval sections of tubes or sacs, which are lined with a single layer of 

 epithelial cells, surrounding a lumen. The cells in the deeper por- 

 tions are usually granular and cubical ; those lining the ducts are 

 generally more columnar in shape and less granular in character. 

 The deeper portions are called the alveoli or acini of the gland, to dis- 

 tinguish them from the ducts, and the character of the epithelium they 

 contain differs according to the function of the gland. Sometimes 

 the cells are so large that they nearly fill the acini, leaving a scarcely 

 perceptible lumen. In other glands the cells are less voluminous 

 and the lumen of each acinus is distinct. It occasionally happens, 

 e.g., in the submaxillary glands, that the acini contain two sorts of 

 cells which secrete different materials. Both kinds of cell may be 

 present in the same acinus, or each kind may be confined to differ- 

 ent acini. In studying sections of glands it must be borne in mind 

 that the tangential section of an acinus would appear as a group of 



