438 TRYPSIN AND TRYPSINOGEN. [BOOK 11. 



transparent material lodged in the spaces of the cell-substance, 

 which material even if not exactly identical with at least closely 

 resembles the mucin found in the secretion; and apparently, in 

 the act of secretion the granules do undergo some such change. 

 In the case of some other glands moreover we have chemical 

 as well as optical evidence that the material stored up in the 

 cell, is, in part at least, not the actual substance appearing in the 

 secretion but an antecedent of that substance. 



An important constituent of pancreatic juice is, as we shall see 

 later on, a body called trypsin, a ferment very similar to pepsin, 

 acting on proteid bodies and converting them into peptone and other 

 substances. Though in many respects alike, pepsin and trypsin are 

 quite distinct bodies, and differ markedly in this, that while an 

 acid medium is necessary for the action of pepsin, an alkaline 

 medium is necessary for the action of trypsin ; and accordingly the 

 pancreatic juice is alkaline in contrast to the acidity of gastric 

 juice. Trypsin can, like pepsin ( 205), be extracted with gly- 

 cerin from substances in which it occurs; glycerin extracts of 

 trypsin however need for the manifestation of their powers the 

 presence of a weak alkali, such as a 1 p.c. solution of sodium 

 carbonate. 



Now trypsin is present in abundance in normal pancreatic 

 juice ; but a loaded pancreas, one which is ripe for secretion, and 

 which if excited to secrete would immediately pour out a juice rich 

 in trypsin, contains no trypsin or a mere trace of it ; nay even a 

 pancreas which is engaged in the act of secreting contains in its 

 actual cells an insignificant quantity only of trypsin, as is shewn 

 by the following experiment. 



If the pancreas of an animal, even of one in full digestion, be 

 treated, while still warm from the body, with glycerin, the glyce- 

 rin extract, as judged of by its action on fibrin in the presence 

 of sodium carbonate, is inert or nearly so as regards proteid bodies. 

 If, however, the same pancreas be kept for 24 hours before being 

 treated with glycerin, the glycerin extract readily digests fibrin 

 and other proteids in the presence of an alkali. If the pancreas, 

 while still warm, be rubbed up in a mortar for a few minutes 

 with dilute acetic acid, and then treated with glycerin, the 

 glycerin extract is strongly proteolytic. If the glycerin extract 

 obtained without acid from the warm pancreas, and therefore inert, 

 be diluted largely with water, and kept at 35 C. for some time, 

 it becomes active. If treated with acidulated instead of distilled 

 water, its activity is much sooner developed. If the inert glyce- 

 rin extract of warm pancreas be precipitated with alcohol in 

 excess, the precipitate, inert as a proteolytic ferment when fresh, 

 becomes active when exposed for some time in an aqueous solution, 

 rapidly so when treated with acidulated water. These facts shew 

 that a pancreas taken fresh from the body, even during full 

 digestion, contains but little ready-made ferment, though there is 



