418 OP FOOD, AND THE DIGESTIVE PROCESS. 



disintegration. The most characteristic feature of the gastric fluid is its decided 

 acidity, which is very perceptible to the taste. With regard to the nature of 



Fig. 126. 



Appearance of the lining membrane of the Stomach, in an injected preparation: A, from the convex surface 

 of the rugse ; B, from the neighborhood of the pylorus, where the orifices of the gastric follicles occupy the 

 interspaces of the deepest portions of the vascular network. 



the acid, however, there has been much discrepancy of opinion amongst Chem- 

 ists; for, simple as the problem of its determination might seem, yet it is com- 

 plicated by the very peculiar property which lactic acid possesses of decomposing 

 the alkaline chlorides at a certain elevation of temperature, the degree being partly 

 determined by the strength of the solution. Hence, supposing lactic acid to be 

 present in the stomach with chloride of sodium, the fluid which passes over by 

 distillation will at first be destitute of hydrochloric acid; but, as the liquor 

 becomes more concentrated, and the temperature rises, hydrochloric acid will 

 appear. This, it has been alleged by Bernard, R. D. Thomson, Lehmann, and 

 other Chemists, is the true source of the hydrochloric acid which may be always 

 obtained from the gastric juice by this process; and it is affirmed by them that 

 Lactic acid is the real agent in the solvent process to which that fluid is sub- 

 servient, the presence of free lactic acid in the stomach having been determined 

 by other means. But, however true this conclusion may be in regard to dogs 

 and pigs, which are the animals that have been chiefly experimented on for this 

 purpose, there appears to be valid evidence that it is not applicable to Man. In 

 the first place, the great readiness with which hydrochloric acid was obtained 

 by Prof. Dunglison from the pure gastric fluid drawn from the stomach of 

 Alexis St. Martin, and the fact that the smell of hydrochloric acid might be 

 distinctly recognized in the fresh juice, 1 are strong evidences in favor of the 

 belief that (as originally maintained by Dr. Prout) free hydrochloric acid is 

 present in this fluid, and that it is the principal if not the only source of its 

 acidity. And an opportunity having been recently afforded to Dr. Bence Jones 

 of obtaining pure gastric fluid, and this having been placed in the hands of Prof. 

 Graham for examination, this distinguished Chemist has succeeded in separating 

 hydrochloric acid from it by his method of " liquid diffusion," which is not open 

 to the objection that applies to distillation; and although he has found free lactic 

 acid to be also present, its quantity is comparatively small. 8 The truth appears 

 to be, that both the hydrochloric and lactic acids may give to the gastric fluid 

 the peculiar solvent power, which (as will be presently shown) it possesses for 

 albuminous substances, and that one may take the place of the other; so that 



1 See Prof. Dunglison's "Human Physiology," 7th edit., vol. i. pp. 585-6. 



2 For his knowledge of this fact, the Author is indebted to Prof. Graham. That hydro- 

 chloric acid is the source of the acidity of the gastric juice has also been maintained by 

 Enderlin("Canstatt's Jahresbericht," 1843, p. 149), and recently by Hiibbenet ("Disqui- 

 sitiones de Succo Gastrico," diss. inaug., Dorpat, 1850. 



