290 THE HUMAN BODY. 



The pancreas, like the majority of the glands connected 

 with the alimentary canal, has an intermittent activity, de- 

 termined 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 micro- 

 scopically, we get specimens of what we may call the " rest- 

 ing gland " a gland which has not been secreting for some 

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

 ing 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 granules 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 it has a good appetite 

 and be then allowed to eat as much meat as it will, the animal 

 will commonly take so much that the stomach will only be emp- 

 tied 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 in which its activity is 

 very little, but during which it is abundantly supplied with 

 food-materials. The pancreas taken from an animal at the 

 end of the first period and prepared for microscopic exami- 

 nation will be found different from that taken from a dog 

 killed at the end of the second digestion period, and also 

 from the resting gland. Towards the end of the period of 

 active work the gland-cells are diminished in size and the 

 proportions of the granular and non-granular zones are quite 

 altered. The latter now occupies most of the cell, while 

 the granular non-staining inner zone is greatly diminished. 

 During the secretion there is, therefore, a growth of the non- 

 granular and a destruction of the granular zone; and the 

 latter process rather exceeding the former, the whole secret- 

 ing cell is diminished in size. During the second digestive 

 period, when secretion is languid, exactly a reverse process 

 takes place. The cells increase in size so as to become larger 

 than those of the resting gland; and this growth is almost 



