

INFLUENCE OF NERVES ON SECRETION. 269 



one portion immediately minced and extracted with glyce- 

 rine, while the other is laid aside for twenty-four hours in 

 a warm place and then similarly treated, it will be found 

 that the first glycerine extract has no power of digesting 

 proteids, while the second is very active. In other words 

 the fresh gland does not contain trypsin, but only some- 

 thing which yields it under some conditions; among 

 others, on being kept. The inactive glycerine extract of 

 the fresh gland is however rich in trypsogen: for if a little 

 acetic acid be added to it, trypsin is formed and the extract 

 becomes powerfully digestive. 



We may then sum up the life of pancreas cell in this 

 way. It grows by materials derived from the blood and 

 first laid down in the non-granular zone. This latter, in 

 the ordinary course of the cell-life, gives rise to the granu- 

 lar zone; and in this is a store of trypsogen produced by 

 the nutritive metabolisms of the cell. When the gland 

 secretes, the trypsogen is converted into trypsin and set free 

 in the secretion; but in the resting gland this transforma- 

 tion does not occur. During secretory activity therefore 

 the chemical processes taking place in the cell, are different 

 from those at other periods; and we have next to consider 

 how this change in the mode of life of the cells is brought 

 about. 



Influence of the Nervous System upon Secretion. 

 When the gland is active it is fuller of blood than when at 

 rest: its arteries are dilated and its capillaries gorged so 

 that it gets a brighter pink color; this extra blood-supply 

 might be the primary cause of the altered metabolism. 

 Again, the activity of the pancreas is under the influence 

 of the nervous system, as evinced not only by the reflex 

 secretion called forth when food enters the stomach, but 

 also by the fact that electrical stimulation of the medulla 

 oblongata will causo the gland to secrete. The nervous 

 system may, however, only act through the nerves governing 

 the calibre of the gland arteries, and so but indirectly on 

 the secreting cells; while on the other hand, it is possible 

 that nerve-fibres act directly upon the gland-cells and, con- 

 trolling their nutritive processes, govern the production of 



