94 PHYSIOLOGY CHAP. 



At the commencement of secretion, the cells of the tubular alveoli 

 undergo gradual changes which become very conspicuous. As is 

 partly shown in Fig. 32, the cells shrink in consequence of 

 secretion. The polyhedral cells become rounder ; the outlines of 

 the cells, which in the resting state are to a large extent invisible, 

 are well marked after secretion, with a double contour; the 

 granules of the outer zone move towards the lumen of the duct, 

 become smaller, less shining, and gradually disappear altogether. 

 It is therefore the secretory matter elaborated into granules by 

 the metabolic activity of the cells which dissolves and passes into 

 the secretion, and not the protoplasmic substance of the inner 

 zone of cells. 



In spite of much research little is known precisely as to 

 the significance of the granules pointed out by Claude Bernard 

 and commonly known as zymogen granules, or their relation with 

 the functional phases of the gland. Kolliker, Henle, v. Frey, and 

 others who observed them before Bernard, regarded them simply 

 as fat - granules, owing perhaps to their round and refracting 

 surface. 



If fragments of the pancreas are dissociated and pounded up 

 in a drop of serum, the granules are set free, and float for a long 

 while in the fluid before they dissolve. On adding acetic acid 

 they dissolve instantly, while in a solution of potash they first 

 swell and then dissolve slowly. Heidenhain, who (as we have 

 seen) observed variations in the number and arrangement of the 

 granules during the various stages of digestion, suggested that 

 they might consist of masses of pro-ferment. This hypothesis 

 was accepted by many authors who gave them the name of 

 zymogen granules. 



But while the participation of the granules in the pancreatic 

 secretion is beyond doubt, there are certain observations which forbid 

 us to accept without further demonstration that they represent 

 the zymogen, or the whole zymogenic content of the gland. 



Liversedge, Laguesse and Debeyre observed that maceration of 

 the pancreas with solutions capable of dissolving the granules 

 (acetic acid or alkali) yields an extract that is completely inactive 

 to protein, even on the addition of kinase which ought to activate 

 it (see Vol. I. p. 30). 



On the other hand, U. Lombroso observed that 10 to 12 days 

 after ligation of the ducts, the pancreas of the pigeon, which no 

 longer shows any granules under the microscope, still exhibits 

 well-preserved enzymatic properties (amylolytic activity). 



VIII. Alkaline while living, the pancreas after death gives 

 an acid reaction, which is probably due to the development of 

 lactic acid, and of fatty acids. 



Chemical analysis of pancreatic tissue shows the presence of 

 an albumin, several globulins, nuclein and nucleo-protein (Spitzer), 



