THE ACTION OF GLAND-CELLS. 267 



detritus forms the secretion; the cells being replaced by new 

 ones constantly formed within the gland. In such cases 

 the secretion is the ultimate product of the cell life; the 

 result of degenerative changes of old age occurring in it. 



In other cases, however, the liberation of the specific 

 element is not attended with the destruction of the secret- 

 ing cell; as an example we may take the pancreas, which 

 is a large gland lying in the abdomen and forming a secre- 

 tion used in digestion. Among others, this secretion pos- 

 sesses the power, under certain conditions, of dissolving 

 proteids and converting them into dialyzable peptones 

 (p. 11). This it owes to a specific element known as tryp- 

 sin, the formation of which within the gland-cells can be 

 traced with the microscope. 



The pancreas, like the majority of the glands connected 

 with the alimentary canal, has an intermittent activity; 

 determined by the presence or absence of food in various 

 parts of the digestive tract. If the organ be taken from a 

 recently killed dog which has fasted thirty hours and, after 

 proper preparation, be stained with carmine and examined 

 microscopically, we get specimens of what we may call the 

 " resting gland " a gland which has not been secreting for 

 some time. In these it will be seen that the cells lining the 

 secreting recesses present two very distinct zones; an outer 

 next the basement membrane which combines with the 

 -coloring matter and is not granular, and an inner which is 

 granular and does not pick up the carmine. The gran- 

 ules we shall find to be indications of the presence of a 

 trypsin-yielding substance, formed in the cells. 



If another dog be kept fasting until he has a good appe- 

 tite and be then allowed to eat as much meat as he will, he 

 will commonly take so much that the stomach will only be 

 emptied at the end of about twenty hours. This period 

 may, so far as the pancreas is concerned, be divided into 

 two. From the time the food enters the stomach and on 

 for about ten hours, the gland secretes abundantly; after 

 that the secretion dwindles, and by the end of the second 

 ten hours has nearly ceased. We have, then, a time during 

 which the pancreas is working hard, followed by a period 



