THE KINDS OF GLANDS. 129 



preliminary to absorption, and so we speak of different kinds 

 of digestions; as that of starch, of fats, of albuminous bodies, 

 and so forth. 



Glands are hollow organs which make or secrete peculiar 

 fluids and poar them out on some free surface of the body. 

 They are very widely distributed; we find, for example, 

 digestive glands (of several kinds) opening into the digestive 

 tube, perspiratory glands opening in the skin, tear glands 

 or lachrymal glands pouring out their secretion on the eye- 

 ball. Different glands have their cavities lined by different 

 kinds of cells, and produce different secretions. In general 

 arrangement all glands are built on one or other of two 

 primary structural plans, known as the tubular and the 

 racemose. 



The Kinds of Glands. All portions of the body making 

 and pouring forth secretions are not technically called 

 glands. In the peritoneum, which lines the inside of the 

 abdominal cavity (p. 11), we find simply a thin membrane 

 (A, Fig. 40), having on its side nearer the cavity which it 

 surrounds a layer of cells, a, and on its deeper side a net- 

 work of very fine blood-vessels, c, supported by connective 

 tissue, d. Such simple, smooth, secreting surfaces are not 

 common; in most cases an extended area is required to 

 form the necessary amount of secretion, and if this were 

 attained simply by spreading out flat membranes, these, 

 from their number and extent, would be hard to pack con- 

 veniently in the body. Accordingly, in most cases, a large 

 area is obtained by folding the secreting surface in various 



"Why do we speak of different kinds of digestion? Illustrate. 

 What is a gland? Give examples of glands. How do glands differ? 

 What are the two chief types of glands named? 



Name aud describe a secreting surface which is not technically 

 called a gland. What is gained by folding a secreting surface? 



