546 MECHANISM OF SECRETION OF PANCREATIC JUICE. 



beyond this. In another series of experiments the animals were fed 

 with peptone (Chapoteaux). This, according to Chischin, was equivalent 

 to reviewing the later stages of digestion, from the time when peptone 

 began to be formed in any quantity in the stomach. The noticeable 

 point about the results in these last cases is, that there is presented a 

 great contrast to feeding with such a primary proteid as egg-albumin. 

 With peptone, the juice becomes secreted in large quantities at once, 

 its acidity is high, and its digestive power well marked. 



It is obvious, therefore, that the nature of the food has an important 

 influence on the course and nature of the secretion. This has been 

 drawn attention to by Khigine, 1 who classes the different foods 

 mentioned above in different orders. He has also pointed out that the 

 amount of juice secreted is not necessarily proportional to its acidity 

 or its digestive power. These, again, are not necessarily proportional 

 to each other, as is shown in the case of bread as food, when a low 

 acidity in the secreted juice is shown, but a high degree of peptic 

 power ; whereas with milk a high degree of acidity is shown, but a much 

 lower degree of digestive power. Finally, the duration of the digestive 

 process is out of all relation to the strength of the secreted juice. It is 

 impossible, then, to draw up any regular scheme of the course of digestion, 

 except so far as specific foods are concerned, observations based upon the 

 course of digestion of foods mixed in arbitrary proportions being of but 

 little value. 



THE MECHANISM OF PANCREATIC SECRETION. 



The histological appearances of the different secretory condi- 

 tions of the pancreas. The pancreas consists of secretory alveoli, 

 between which are here and there seen masses of cells of a different 

 character, and having no connection with the proper secretory channels 

 of the gland. These masses of cells are presumably not connected with 

 the ordinary processes of the secretion of a digestive juice, and the follow- 

 ing account will therefore be confined to the typical secretory alveoli. 



If a small portion of the pancreas of an animal be examined in the 

 living state, it will be found to consist of many secretory alveoli, and 

 these secretory alveoli of cells contain numbers of discrete granules. 

 It is generally found that whatever digestive stage the animal is in, there 

 exists an outer zone in the alveolus free from granules. This is not, 

 however, invariably the case. Ordinary stains, such as hrematoxylin 

 and carmine, are found to colour this outer zone more deeply than the 

 rest. This is in conformity with the usual rule, that such stains do not 

 deeply colour the secretory granules of cells, or the substance formed by 

 their breaking down. If the cells are macerated for a few days in 

 neutral ammonium chromate, a radial fibrillation is revealed 2 in this 

 outer zone. The addition of water to the fresh gland causes the 

 granules to disappear, and dilute alkalies produce this result even more 

 rapidly. Acids, either mineral or organic, cause the distinction between 

 the two zones to be lost, the whole cell becoming clear. By hardening 

 the gland in solutions of osmic acid, or in the vapour of osmic acid, the 

 granules may be preserved. 



1 " Etudes sur 1'excitabilite' secretoire specifique de la muqueuse du canal digestif" 

 Arch, de, sc. bioL, St. Petersbourg, 1895, vol. iii. p. 5. 



2 Heidenhain, Hermann's "Handbuch," Bd. v. Abth. 4. 



