156 OF FOOD, AND THE DIGESTIVE PROCESS. 



108. The most characteristic feature of the Gastric Juice is its decided 

 acidity, which is very perceptible to the taste, and is constant throughout 

 the animal kingdom. With regard to the nature of the acid, however, there 

 has been much discrepancy of opinion amongst Chemists; for simple as the 

 problem of its determination might seem, it is complicated by the very pe- 

 culiar property which lactic acid possesses, of decomposing the alkaline 

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

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

 be present in the stomach with sodium chloride, 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 and other Chemists, 

 is the true source of the hydrochloric acid which may be always obtained 

 from the gastric juice by this method; and it is affirmed by them that lactic 

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

 vient, the presence of free lactic acid in the stomach having been deter- 

 mined by other means. In like manner, Dr. F. G. Smith, 1 on examining the 

 contents of the stomach of Alexis St. Martin, two and a half hours after a 

 small quantity of bread had been eaten, obtained evidence of the presence 

 of lactic, and of the absence of all but the slightest trace of hydrochloric acid. 

 [These experiments have since been confirmed by Dr. Robert M. Smith in 

 some investigations made in the Physiological Laboratory of the University 

 of Pennsylvania, upon the contents of the stomach of a recently executed 

 criminal. In these experiments, lactic acid was undoubtedly present, while 

 no trace of free hydrochloric acid could be detected. Phila. Med. Times, 

 Feb. 13th, 1875.] On the other hand, the great readiness with which hydro- 

 chloric acid was obtained many years ago by Prof. Dunglisou from the pure 

 gastric fluid drawn from the stomach of Alexis St. Martin, and the fact that 

 the smell of hydrochloric acid may be distinctly recognized in the fresh 

 juice, 2 are strong evidences in favor of the belief that (as originally main- 

 tained 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 afforded to Dr. Bence Jones, of obtaining a fluid continually 

 vomited in large quantities from the stomach of a patient affected with Sar- 

 cina ventriculi, and this fluid, which presented all the ostensible characters 

 of gastric juice, having been placed in the hands of Prof. Graham for ex- 

 amination, this distinguished Chemist 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 found free lactic acid 

 to be also present, its quantity was comparatively small. 3 It appears, then, 

 to be a reasonable conclusion, that whilst hydrochloric acid is originally 

 poured forth, and is therefore the acid obtained by those experimenters, who 

 have employed mechanical irritation to the empty stomachs; other acids, as 

 the lactic, butyric, or even acetic, may be formed during digestion, and may 

 thus have been obtained by those who have examined the contents of the 

 stomach only during or towards the close of that process. Allowance must also 

 be made for differences existing in different animals, and perhaps also at 



1 Experiments upon Digestion, Philadelphia, 1856. 



2 See Prof. Dunglison's Human Physiology, 8th edit , vol. i, p. 152. 



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

 hydrochloric acid is the source of the acidity of the gastric juice has also been main- 

 tained by Enderlin (Canstatt's Jahresbericht, 1843, p. 149), by Hubbenet (Dis()iiisi- 

 tionos de Succo Gastrioo, Diss. inaug., Dorpat, 1850), by Bidder and Schmidt (Die 

 Vcrdauungssaefte und der Stoffwcchsel), and by Gruencwaldt and Schroeder in their 

 Theses on this subject. 



