CHAP, i.] DIGESTIOX. 271 



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- 

 rine 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 

 present in it a body which, by some kind of decomposition, gives 

 birth to the ferment. ^ We may remark incidentally that though the 

 presence of an alkali is essential to the proteolytic action of the 

 actual ferment, the formation of the ferment out of its forerunner 

 is favoured by the presence of a small quantity of acid. To this 

 body, this mother of the ferment which has not at present been 

 satisfactorily isolated, the name of zymogen has been applied. 

 But it is better to reserve the term zymogen as a generic name 

 for all such bodies as not being themselves actual ferments, may 

 by internal changes give rise to ferments, for all 'mothers of 

 ferment' in fact; and to give to the particular mother of the 

 pancreatic proteolytic ferment, the name trypsinogen. 



The pancreatic cell then contains trypsinogen ; and now comes 

 the important observation that the amount of trypsinogen in a 

 pancreas at any given time rises and sinks pari passu with the 

 granular inner zone, i.e. with the amount of granular substance in 

 the cell. The wider the inner zone and the more abundant the 

 granules the larger the amount, the narrower the zone and the 

 fewer the granules the smaller the amount, of trypsinogen ; and in 

 the cases of old-established fistulae, where the secretion is wholly 

 inert on proteids, the inner granular zone is absent from the 

 cells. 



We have no corresponding satisfactory information concerning 

 the history of any zymogen which may be supposed to belong to 

 the amylolytic ferment of the pancreas or to the ferment which 

 acts upon fats. Nor on the other hand are we in a position to say 

 that the granules are wholly composed of trypsinogen; but it seems 

 clear that they contain trypsinogen, and that their abundance or 

 scarcity afford a measure of the quantity of that substance present 

 in the cell. 



Hence we may draw a parallel between the mucous cell and 

 the pancreatic cell. Just as the protoplasm of the former by its 

 metabolism manufactures mucigen, so the protoplasm of the latter 

 by its metabolism manufactures trypsinogen, and just as the 

 mucigen gives rise to mucin which escapes from the cell to form 

 part of the actual secretion, so also the trypsinogen gives rise to 

 trypsin, which similarly forms part of the pancreatic juice. Just as 

 with the disappearance of the mucigen the protoplasm grows with 



