324 A MANUAL OF PHYSIOLOGY 



proteolytic power of an extract of the pancreas, or the 

 gastric mucous membrane, seems to be, roughly speaking, 

 in proportion to the quantity of granules present in the cells. 

 Therefore it is concluded that the granules are related in 

 some way to trypsin and pepsin. 



But we should greatly deceive ourselves if we supposed 

 that granules of this nature in gland-cells are necessarily 

 related to the production of ferments. The mucigenous 

 granules have no such significance. Most digestive secre- 

 tions contain proteid constituents, with which the granules 

 may have to do, as well as with ferments. And bile, a 

 secretion which contains no mucin, no proteids, and no 

 ferments, as essential constituents, is formed in cells with 

 granules so disposed and so affected by the activity of the 

 gland as to suggest some relation between them and the 

 process of secretion. In the liver - cells of the frog, in 

 addition to glycogen and oil-globules, small granules may 

 be seen, especially near the lumen of the gland tubules; 

 they diminish in number during digestion, when the secre- 

 tion of bile is active, and increase when food is withheld and 

 secretion slow. And in fasting dogs the secreting cells oi 

 Brunner's glands, the pyloric glands and the pancreas, as 

 , well as the lining epithelium of the bile-ducts, have been 

 found to contain many fatty granules. Possibly some of 

 these represent the fat which is known to be excreted into 

 the alimentary canal (pp. 372, 374, 455). 



The granules in the ferment - forming glands are not 

 composed of the actual ferments, and, indeed, the actual 

 ferments are present in the secreting cells only in small 

 amount, if at all, as is shown by the following facts : 



A glycerine extract of a fresh pancreas has hardly any 

 effect on proteids ; a similar extract of a stale pancreas is 

 very active. Therefore the fresh pancreas is devoid of 

 trypsin. But it contains a substance which can readily 

 be changed into trypsin ; and this substance is soluble in 

 glycerine, for the inert extract becomes active when it is 

 treated with dilute acetic acid, or even when it is diluted 

 with water and kept at the body-temperature. If the fresh 

 pancreas be first treated with dilute acetic acid, and then 

 with glycerine, the extract is at once active. AH this goes 



