DIGESTION. 199 



this secretion on nutritive bodies have not as yet yielded any 

 positive results. 



IV. Pancreas Gland and Pancreatic Juice. 



In invertebrata, which have no pepsin digestion and which also 

 have no formation of bile, the pancreas, or at least an analogous 

 organ, seems to be the essential digestion gland. On the contrary, an 

 anatomically characteristic pancreas is absent in certain vertebrata 

 and in certain fishes. Those functions which should be performed 

 by this organ seem to be performed in these animals by the liver, 

 which may be rightly called HEPATOPANCREAS. In man and in most 

 vertebrata the formation of bile and of certain secretions containing 

 enzymes important for digestion is divided between the two organs, 

 the liver and the pancreas. 



The pancreas gland is similar in certain respects to the parotid 

 gland. The elements secreted by the former consist of nucleated 

 cells whose basis forms a mass rich in albumin, expand in water 

 and in which two distinct zones exist. The outer zone is more 

 homogeneous, the inner cloudy due to a quantity of granular, 

 substance. The nucleus lies about midway between the two zones, 

 but this position may change with the varying relative size of the 

 two zones. According to HEIDENHAIN, the inner part of the cells 

 diminishes in size during the first stages of digestion, in which the 

 secretion is active, while at the same time the outer zone enlarges 

 owing to the absorption of new material. In a later stage, when 

 the secretion has decreased and the absorption of the nutritive 

 bodies has taken place, the inner zone enlarges at the expense of 

 the outer, the substance of the latter having been converted into 

 that of the former. Under physiological conditions the glands are 

 undergoing a constant change, at one time consuming from the 

 inner part and at another time growing from the outer part. The 

 inner granular zone is converted into the secretion, and the outer, 

 more homogeneous zone, which contains the repairing material, is 

 then converted into the granular substance. 



Besides considerable quantities of proteids, globulin, nucleo- 

 albumin, and albumin, we find in this gland three enzymes, or, 



