NATURE OF CHYMIFICATION. 341 



which the food is dissolved in the Gastric fluid is of a purely Chemical nature, 

 since it takes place out of the living body as well as in it, allowance being 

 made for the difference in its physical condition. That the natural process of 

 digestion is imitated, when the food is submitted to the action of the gastric 

 juice in a vial, not only in regard to the disintegration of its particles, but as 

 to the change of character which they are made to undergo, is proved by the 

 fact, that the artificial chyme thus formed exhibits the same changes as the 

 real chyme, when submitted to the action of the bile ( 446). The process 

 of digestion, however, may be freely conceded to be vital, in so far as it is 

 dependent upon the agency of a secreted product, which vitally alone (so far 

 at least as we at present know) can elaborate ; and all for which it is here 

 contended is, that, when this product is once formed, it has an agency upon 

 the alimentary matter, which, though not yet fully understood, is conformable, 

 in all that is known of its operation, to the ordinary laws of chemistry. Thus, 

 Digestion is conformable to Chemical solution, -first, in the assistance which 

 both derive from the minute division of the solids submitted to it ; secondly, 

 in the assistance which both derive from the successive addition of small por- 

 tions of the comminuted solid to the solvent fluid, and from the thorough inter- 

 mixture of the two by continual agitation; thirdly, in the limitation of the 

 quantity of food on which a given amount of gastric juice can operate, which 

 is precisely the case with chemical solvents; fourthly, in the assistance 

 which both derive from an elevation of temperature,* the beneficial influence 

 of heat being only limited, in the case of digestion, by its tendency to produce 

 decomposition of the gastric fluid ; -fifthly, in the different action of the same 

 solvent upon the various solids submitted to it. 



455. We have now to inquire what information has been obtained, with 

 regard to the chemical nature of the organic principle, which performs so 

 important a part in the digestive process. It may be considered a well-esta- 

 blished fact, that diluted acids alone have no power of chymifying alimentary 

 substances, although capable of partially dissolving some of them ; but that 

 their presence in the gastric fluid is essential to its effectual action. Thus 

 Muller states that, when small pieces of meat, or small cubes of coagulated 

 white of egg, have been macerated for some time in equal quantities of much- 

 diluted muriatic, acetic, tartaric, and oxalic acids, a precipitate or turbidity 

 may be produced by the ordinary re-agents ; but that the masses are not per- 

 ceptibly changed, the cubes of coagulated white of egg preserving their angles 

 and edges for weeks. Small pieces of meat were also placed in a solution of 

 common salt, and submitted to the action of a powerful galvanic battery, which 

 would set free muriatic acid ; without the change being perceptibly accele- 

 rated. From the subsequent experiments of Eberle and Schwann, however, 

 it appears that, although acids alone have so little power of digesting food, 

 they act energetically when combined with mucus of the stomach.t The 

 following is an outline of these experiments. The mucous membrane of the 

 fourth stomach of the calf, being dissected from the other coats, and washed 

 with cold water until it no longer gives evidence of containing a free acid, is 

 macerated in water acidulated with muriatic acid; and after some time, the 



* The influence of temperature is remarkably shown in some of Dr. B.'s experiments. 

 He found that the gastric juice had scarcely any influence on the food submitted to it, 

 when the bottle was exposed to the cold air, instead of being kept at a temperature of 

 100. He observed on one occasion, that the injection of a single gill of water at 50 

 into the stomach, sufficed to lower its temperature upwards of 30; and that its natural 

 heat was not restored for more than half an hour. Hence the practice of eating ice after 

 dinner, or even of drinking largely of cold fluids, is very prejudicial to digestion. 



f By Eberle it was stated that the acidulated mucus of any membrane is an efficient 

 solvent; but this has been found by Muller and Schwann to be an error, only the mucus 

 of the stomach possessing this property. 



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