

THE SECRETORY TISSUES AND ORGANS. 291 



entirely due to the granular zone which now occupies most 

 of the cell. 



These facts suggest that during secretion the granular 

 part of the cells is used up : but that, simultaneously, the 

 deeper non - granular zone, being formed from materials 

 yielded by the blood, gradually renews the granular. Dur- 

 ing active secretion the breaking down of the latter to 

 yield the specific element occurs faster than its regenera- 

 tion; in a later period, however, when the secretion is ceas- 

 ing, the whole cell grows and, especially, the granular zone is 

 formed faster than it is disintegrated; hence the great in- 

 crease of that part of the cell. If this be so, then we ought 

 to find some relationship between the digestive activity of an 

 infusion or extract of the gland and the size of the granular 

 zones of the cells; and it has been shown that such exists; 

 the quantity of trypsin which can be obtained from a pan- 

 creas being proportionate to the size of that portion of its 

 cells. 



The trypsin, however, does not exist in the cells ready 

 formed, but only a body which yields it under certain cir- 

 cumstances, and called trypsinogen. 



If a perfectly fresh pancreas be divided into halves and 

 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 something which 

 yields it under some conditions; among others, on being 

 kept. The inactive glycerine extract of the fresh gland is, 

 however, rich in trypsinogen : 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 a 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 ordi- 

 nary course of the cell-life, gives rise to the granular zone; 

 and in this is a store of trypsinogen produced by the active 

 metabolisms of the cell. When the gland secretes, the tryp- 

 sinogen is converted into trypsin and set free in the secre- 

 tion; but in the resting gland this transformation does not 

 occur. During secretory activity, therefore, the chemical 



