CHAP. III.] IS THERE A ZYMOGEN OF THE DIASTATIC ENZYME ? 207 



ferment is liberated, perhaps by a process of dissociation, may be 

 extracted from the pancreas, and solutions of it are found not to 

 possess proteolytic properties^ though they may acquire these by 

 the action of certain external agents. This antecedent of the 

 ferment has been termed by Heidenhain, Zymogen. In discussing 

 the origin of pepsin we have already referred to evidence which 

 appears to shew that in the case of that enzyme also there probably 

 exists an antecedent (which some have even named Pepsinogen) 

 which does not possess proteolytic properties but which acquires these, 

 for example on treatment with acids. We have also adduced facts 

 which prove the existence of a zymogen of the rennet-ferment. 



It is probable that what is certainly true of the proteolytic ferment 

 of the pancreas may be true of its diastatic ferment, and we may ask 

 ourselves, Is there any evidence in support of an antecedent or 

 zymogen of this ferment ? 



Two years before Heidenhain 1 published the re- 

 me^somver~ mar kable paper, rich in fresh facts, in which he 

 Sdge point to announced his discovery of the zymogen of the proteo- 

 the existence lytic ferment, Liversidge, working in Foster's laboratory, 

 of a zymogen had published facts, which have not received the notice 

 atic^dSatic which the y deserve, and which point, as the Author 

 enzyme * thinks, to the probable existence in the pancreas of an 



antecedent of the diastatic ferment. 



Liversidge removed the diastatic ferment from the pancreas by 

 long-continued washing in water. The minced pancreas which had 

 been thus exhausted was transferred to a filter and allowed to 

 remain exposed to the air for a few hours, when, on again treating 

 it with a small quantity of distilled water, a very active diastatic 

 solution was obtained. Again, he shewed that in order to exhaust 

 minced pancreas of its diastatic ferment by the action of glycerin, 

 contact of large quantities of glycerin during fourteen months was 

 necessary. The pancreatic tissue which had been rendered thus 

 inactive, after standing on a muslin filter for six hours, readily gave, 

 not only an active aqueous extract, but also yielded an active glycerin 

 solution 2 . 



At the same .time there are two points in connection with this 

 question which should be borne in rnind. (1) In the above experi- 

 ments it can hardly be regarded as absolutely certain that the 

 diastatic action exerted by the pancreas after exposure was not due 

 to bacteria. (2) The zymogens of trypsin, pepsin, and of the rennet- 

 ferment are all soluble in water (or water containing a little salt) ; 

 in an aqueous extract, the zymogen can be shewn to be present, if 

 when treated in certain ways the solution shews ferment activity. 



1 Heidenhain, 'Beitrage zur Kenntniss des Pankreas,' Pfliiger's Archiv, Vol. x. 

 (1875), p. 557. The part containing this paper was published on June 25th. 



2 Liversidge, 'On the Amylolytic Ferment of the Pancreas' (from the Physiolo- 

 gical Laboratory in the University of Cambridge), Journal of Anatomy and Physiology, 

 Vol. vni. (1874), p. 23. The number of the Journal containing this paper was published 

 in November, 1873. 



