238 DIGESTION. 



tare of 212 Fahr., but it is not coagulated, although it loses its specific properties. It is 

 not affected by acids but is precipitated by tannin, creosote, and a great number of the 

 metallic salts. This substance dissolved in water slightly acidulated possesses, in a very 

 marked degree, the peculiar solvent properties of the gastric juice; but it has been found 

 by Pay en and Mialhe not to be so active as the principle extracted from the gastric juice 

 itself, which is described by Payen under the name of gasterase. In the abattoirs of 

 Paris, Mialhe collected from the secreting stomachs of calves as they were killed, from 

 six to ten pints of gastric juice ; and from this he extracted the pure pepsin by the pro- 

 cess recommended by Payen, which consists merely in one or two precipitations by 

 alcohol. This substance he found to be identical with the principle obtained by Payen 

 from the gastric juice of the dog. Its action upon albuminoid matters was precisely the 

 same as that of pepsin extracted from artificial gastric juice, except that it was more 

 powerful. 



Source of the Acidity of the Gastric Juice. Eeaumur and Spallanzani recognized 

 that the fluid from the stomach has, at certain times, an acid reaction ; and subsequent 

 observations have confirmed this fact and have shown that this reaction is invariable 

 during digestion. But, although the most distinguished and skilful chemists of the day 

 have attempted to ascertain the source of this acidity, from Prout, in 1823, to Blondlot, 

 in 1858, embracing Leuret and Lassaigne, Tiedemann and Gmelin, Berzelius, Chevreul, 

 Bidder and Schmidt, Dumas, Lehmann, Bernard and Barreswil, with a host of others, 

 the question has not yet received a solution which is generally accepted. 



The method made use of by some of those who profess to have found free hydrochloric 

 acid in the gastric juice has been to subject the fluid to distillation, testing the acid fluid 

 which passes over with nitrate of silver ; but the experiments of Bernard and Barreswil 

 on the gastric juice from dogs, and the more recent observations of Dr. F. G. Smith on 

 the gastric juice from St. Martin, have shown that this process is really of little value. 

 The following observations by Bernard and Barreswil seem to show that, although 

 hydrochloric acid may be obtained from gastric juice by distillation, it does not neces- 

 sarily exist in the fluid in a free state ; which is a very important consideration in a ques- 

 tion in which every thing depends upon the absolute accuracy of modes of analyses : 



In subjecting the gastric juice of the dog to distillation at a low temperature, with all 

 the necessary precautions, it was found that the first products did not present an acid re- 

 action. It was at first thought that this would be a ground for the exclusion of hydrochloric 

 acid, which is considered to be volatile ; but it was found that, in the distillation of water 

 which had been slightly acidulated with hydrochloric acid, the first products were neu- 

 tral, and the acid was disengaged only in the fluid which passed over toward the last 

 periods of the process. On again distilling the gastric juice, it was found that the prod- 

 uct was neutral, presenting no precipitate with the nitrate of silver, until about four- 

 fifths of the fluid had passed over ; that afterward, the fluid which passed over was distinct- 

 ly acid, but did not precipitate with the salts of silver ; and " finally, only toward the last 

 instants, when there remained only a few drops of gastric juice to evaporate, the acid 

 liquid which was produced gave a marked precipitate with the salts of silver, which was 

 not dissolved by concentrated nitric acid." It was found that the addition to the gastric 

 juice of a small quantity of oxalic acid produced a marked opacity due to the formation 

 of the insoluble oxalate of lime, while an equal quantity of the same reagent produced no 

 opacity in water containing a proportion of two thousandths of hydrochloric acid, to 

 which chloride of calcium had been added. From this experiment, Bernard concluded 

 that the hydrochloric acid in the gastric juioe exists in the condition of a chloride and 

 not in a free state. 



Prof. F. G. Smith, who had an opportunity of examining the gastric juice from St. 

 Martin, in 1856, took the fluid from the stomach after two ounces of dry bread had been 

 chewed and swallowed, and subjected it to distillation. The first fluid which passed over 



