452 E. ta; ACE CARLIER 



The great fatigue exhibited by thc nuclei of secreting cells during the 

 conveition of zymogen into zymin by the action of dilute acids has for a 

 long time been a puzzle to me, for one would suppose that the manufacture of 

 zymogen would be far more fatiguing than its mère passage out of the cell 

 into the gland lumen. The researches of Maccallum " of Toronto throw 

 light upon this subject. He maintains that zymogen is preceeded by a sub- 

 stance rich in phosphorous and iron, produced at the expense of the chro- 

 matin of the nucleus. This substance he terms proiymogen which becomes 

 united with a constituent of the cell protoplasm to form zymogen. Mourel"-^ 

 also takes a similar view of the production of zymogen and he named the 

 antécédent substance - prezymogen « and Bensley' has corroborated thèse 

 researches in his récent paper on the stomach. 



I believe that the nuclear exhaustion so évident in my spécimens is 

 indeed brought about by the manufacture of prozymogen. Almost directly 

 after the cell has begun to pour out its sécrétion, the nucleus commences 

 to form a new supply of prozymogen at the expense of its store of chroma- 

 tin and that the movement of the chromatin towards the nuclear membrane 

 and its application to its inner surface is of service in facilitating this process, 

 but further believe that the prozymogen is not elaborated into zymogen 

 until the cells hâve practically emptied themselves of the zymogen already 

 formed and hâve begun to take up substances from the blood. Once the 

 formed zymogen is ail removed the cell quickly transforms the prozymogen 

 into nevj zymogen, which is the meaning of the rapid reappearance of the 

 zymogen granules. 



On the other hand the power of the nucleus to manufacture prozymo- 

 gen is limited; once its store of chromatin is reduced to a certain point, 

 it must renew the stock before it can again produce prozymogen. This 

 renewal of chromatin is brought about by the entrance into the nuclear 

 juice of an easily coagulable substance (probably a proteid material amongst 

 other things) which is the meaning of the great increase in the lanthanin 

 granules soon after coinplete exhaustion of the nucleus has occurred and 

 I believe that this necessity for repair sufficiently accounts for the pheno- 

 menon of the double secretory wave, the cell though full of zymogen gra- 

 nules not being in a fit state to secrète again until the nucleus has comple- 

 tely recuperated, but that when once this point is reached, there being no 

 longer any further need of rest, the cell again starts secreting should any 

 call be made upon its énergies. 



