598 DIGESTION. 



although acids alone have little power in digesting food, they act ener- 

 getically, when combined with the mucus of the stomach. Eberle 

 thought, that the acidulated mucus of any membrane would produce the 

 effect, but J. Muller and Schwann found it to be restricted to that of the 

 stomach. The agency of pepsin is regarded by Liebig 1 to be similar 

 to that of diastase in the germination of seeds. Both are bodies in a 

 state of transformation or decomposition; the latter effecting the solu- 

 tion of starch by its conversion into sugar; and the former the forma- 

 tion of alimentary matter into chyme. The present belief amongst 

 physiologists and chemists from all these experiments, as well as 

 those of Wasmann and others is, that pepsin, by inducing a new 

 arrangement of the elementary particles or atoms of alimentary matter, 

 disposes it to dissolve in the gastric acids. Chlorohydric acid, indeed, 

 dissolves wliite of egg by -ebullition, just as it does under the influence 

 of pepsin ; so that pepsin replaces the effect of a high temperature in 

 the stomach. 2 Liebig, consequently, does not believe, that the digestive 

 process is a simple solution, but a species of fermentation, not identical, 

 however, with any of the known processes of fermentation occurring 

 in organic matters out of the body. It differs from ordinary fermen- 

 tation in being unattended with the formation of carbonic acid ; in not 

 requiring the presence of oxygen, and in not being accompanied by 

 the reproduction of the ferment. 3 



The conclusions of MM. Bernard de Villefranche and Barreswil, 4 

 from numerous and varied experiments related to the Academie Royale 

 des Sciences, of Paris, have been referred to already. From these, it 

 would seem, that an organic v compound of like nature exists in the 

 saliva, gastric juice, and pancreatic fluid; and that its digestive powers 

 vary according as it is associated with fluid having an acid or an alka- 

 line reaction. Thus in the gastric juice, which is acid, it readily dis- 

 solves nitrogenized substances, fibrin, gluten, albumen, &c., whilst it 

 is altogether without action on starch. These gentlemen affirm, that 

 if we destroy this acid reaction, and render the gastric juice alkaline 

 by the addition of carbonate of soda, the active organic matter being 

 in presence of an alkaline fluid changes its physiological action, and 

 becomes able to modify starch rapidly, whilst it loses the power of 

 digesting nitrogenized substances. As the saliva and pancreatic juice 

 are alkaline, it w r as interesting to know whether a change in the chemi- 

 cal reaction of these fluids would produce in them the same change of 

 properties as in the case of the gastric juice. Experiment proved such 

 to be the fact. By rendering the pancreatic fluid or saliva acid, their 

 ordinary action was inverted : they acquired the power of dissolving 

 meat and other nitrogenized substances, whilst they lost their influence 

 on starch. 



M. Magendie examined the gases in the stomach and intestines of 

 executed criminals, and obtained the following results : a, in the case 

 of an individual who had taken food in moderation an hour previous to 



1 Animal Chemistry, Gregory and Webster's edit., p. 106, Cambridge, Mass., 1842. 



2 Graham's Elements of Chemistry, Amer. edit., by Dr. Bridges, p. 696, Philad., 1843. 



3 Kirkes and Paget, Manual of Physiology, Amer. edit., p. 173, Philad., 1849. 



4 Comptes Rendus, 9 Decemb., 1844, and 7 Juillet, 1845. 



