GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 257 



possibly out of their own substance, the specific elements 

 in question. Somewhat like a sheep by taking the proper 

 nourishment into its body, and by chemical changes in its 

 tissues, may produce the woolly covering of the skin. 



That the specific elements of glands are thus built out 

 of the cells themselves is especially well shown in the case 

 of the oil glands of the skin. In those glands some of the 

 cells may be seen to grow large, then by internal chemical 

 changes their own substance apparently disintegrates into 

 oil, a change which continues until finally the whole cell 

 falls into pieces, and its debris forms the secretion. In 

 other cells the destruction is not complete, but only por- 

 tions of the cell break up into the secretion in question. In 

 such cases, of course, an individual cell by continuing to 

 grow and continuing to form out of its substance the spe- 

 cific element may remain active for an indefinite time, while 

 in the case of cells where the disintegration is complete, 

 new cells must continually be forming to replace those that 

 break down. 



In the case of the pancreas a complete destruction of 

 the cells does not occur, as it does in the case of the oil 

 gland. To take a not very close analogy, the secretion of a 

 gland is not a product made by the cell in the same sense 

 that a table is a product made by a carpenter, but the secre- 

 tion is a product derived from the cell substance itself, as 

 the table is a product of the oak tree. 



In the case of the pancreas these granules are not, how- 

 ever, identical with its specific element. The main specific 

 element of the pancreas is called trypsin, whose marked 

 influence in digestion will be discussed later. But the 

 granules in the pancreas cells are not trypsin. They are 

 some antecedent substance out of which, however, by slight 

 changes trypsin is produced. The granules are called tryp- 

 sinogen granules; that is, by the etymology of that word, 

 the producers of trypsin. 



Several- fortunate circumstances arise by this arrange- 

 ment. Trypsin is soluble and could not easily be stored up in 

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