170 OF FOOD, AND THE DIGESTIVE PROCESS. 



In the first period of digestion there is a more rapid using up of the in- 

 terior of the cell, and a more rapid addition to the exterior. In the second 

 period, when the greatest changes take place, the homogeneous exterior is 

 metamorphosed into the granular interior; whilst during the stage of 

 hunger, the using up of materials is smaller, the addition of new materials 

 is slower, but it causes visible widening of the exterior portion of the cell. 

 Heidenhain believes that in no other organ are the interior changes 

 shown with such marked microscopic distinctness. He also describes a 

 body obtained from the pancreas, which he calls zymogen, which is soluble 

 in concentrated glycerin without suffering any change. Its conversion 

 into pancreatin occurs in watery solution quicker in warmth, slower at 

 the usual temperature. Acids cause these changes, but salts, such as 

 chloride of sodium and carbonate of soda, retard this metamorphosis. The 

 quantity of this body in the pancreas during digestion varies with the 

 changes in the cell; it increases and decreases according as the degree 

 of formation of the granular interior of the cell increases and decreases. 

 Irritation of the medulla by induction currents increases this secretion prob- 

 ably through its connection with the iutraglaudular ganglia. The secre- 

 tory nerves of the pancreas have a direct influence not only on the amount 

 of water, but of the solid elements in that secretion. Pfliiger's Archives.] 

 Distinct evidence of the indirect influence of the nervous system upon the 

 activity of the gland has been obtained. Section of the nerves accompany- 

 ing the vessels causes congestion of the gland, greatly augments the quantity 

 of the secretion (paralytic secretion), which continues when the animal is 

 kept fasting. If, whilst these nerves are uninjured, the pneumogastrics are 

 divided, and the centric ends excited, the secretion is diminished, and a 

 similar inhibitory effect is observed at the commencement of efforts to vomit. 

 From these facts the conclusion may be drawn that the nerves distributed 

 to the gland exert an inhibitory or restraining influence upon the secretory 

 .activity of the gland, which is removed by reflex action, through the spinal 

 cord and sympathetic nerve, when the pueumogastric, or its peripherical 

 terminations in the stomach, are excited. 1 No evidence has been obtained 

 that any nerves directly excite the secretion. Under the toxic influence of 

 woorara, the secretion is greatly augmented. As the organ is of consider- 

 able size, is very constant amongst the Vertebrata, and uniformly discharges 

 its secretion into the duodenum, it is natural to suppose that it must exert 

 an important influence in preparing the food for absorption ; and this is 

 fully borne out by our knowledge of the serious interference to the due per- 

 formance of this operation, resulting from disease of this organ, and of the 

 extreme instability of the organic matter contained in its secretion. 



120. From the researches of many experimenters, it appears to be well 

 ascertained that probably owing to the presence of three separate ferments, 2 

 the pancreatic juice can 1. Like diastase, convert starch into sugar; 2. 

 That it can emulsify the fats and oils and effect their decomposition into 

 glycerin and the fatty acids; 3. That it can, like pepsin, convert albumen 

 into peptone. 3 Its action differs from pepsin, however, in continuing in 

 alkaline and neutral solutions, whilst it is arrested by a moderate excess of 

 acid. The first and second of the above actions are possessed by all speci- 



1 See Bernstein, Arbeiten uus dor Leipziger Anstalt, 1870, p. 1. 



2 See Danilcwsky, Arrliiv i'. Patli. Aimt., Bd. xxv. 



8 Liversidge and Cluwcs (Journal of Armt. and Phys., vol. viii, p 25) have shown 

 that pepsin and pancreatic ferment have a very similar chemical composition. The 

 percentage composition of the probably impure ferment obtained by maceratinc; the 

 pancreas in alcohol to precipitate the albuminoid compounds, extracting with 

 glycerin and precipitating with alcohol, was C. 34 925, N. 11.020, Ash 15.170; that 

 of Pepsin was C. 39.792, N. 10.100, Ash 10.48. 



