158 DIGESTION. 



Prof. C. Schmidt 1 found the gastric juice of the human subject similar 

 in constitution to the above, except that it contained a larger propor- 

 tion of water and a considerably smaller proportion botli of free acid 

 and pepsine, as well as of solid ingredients generally. From our own 

 repeated observations upon the dog, there is no doubt that both the 

 quantity and density of the gastric juice vary, within certain limits, in 

 different individuals even of the same species the proportion of solid 

 ingredients being less when the secretion is more abundant, and greater 

 when the secretion is in small quantity. 



The most striking physical property of the gastric juice is its acid 

 reaction, which is always strongly marked, and by which it is distin- 

 guished from all the other digestive secretions and internal fluids of the 

 body. This property, as indicated in the foregoing table, depends upon 

 the presence in the secretion of a free acid. Notwithstanding the 

 numerous investigations which have been directed to this point, it is 

 still uncertain whether the reaction of the gastric juice be due to free 

 hydrochloric or free lactic acid ; each of these two substances having 

 been found by different observers. Those who attribute the reaction of 

 the gastric juice to hydrochloric acid (Prout, Dunglison, Enderlin, 

 Bidder and Schmidt) depend upon its being obtainable by distillation, 

 and more especially upon a quantitative determination of all the alka- 

 line and earthy bases contained in the secretion, and an estimate of 

 the amount of hydrochloric acid necessary to saturate these bases ; the 

 hydrochloric acid, actually obtainable, being found to be more than 

 sufficient to unite with the above bases in neutral combination. On the 

 other hand, various experimenters (Lehmann, Leuret, Lassaigne, Francis 

 G. Smith, Bernard and Barreswil) have not only found evidences of 

 the presence of free lactic acid in the gastric juice, but some of them 

 have also shown 3 that during distillation the concentrated lactic acid 

 would set free hydrochloric acid by decomposition of the alkaline chlo- 

 rides, although none were originally present in the fluid. They also 

 point out that the addition of a small quantity of oxalic acid to the 

 gastric juice produces a precipitate of lime oxalate, while no such pre- 

 cipitation will take place in a fluid containing two parts per thousand 

 of free hydrochloric acid. It is certain, however, that either of these 

 acids may replace that which naturally exists in the gastric juice with- 

 out essentially impairing its digestive properties. 



The remaining important ingredient of the gastric juice is its albu- 

 minoid matter, known under the name of pepsine. This substance is 

 not precipitated by either the organic or the mineral acids, but is thrown 

 down by the action of heat and by alcohol in excess. It may also be 

 precipitated, like ptyaline, from its watery solution acidulated with 

 dilute phosphoric acid, by the addition of lime water ; the precipitated 

 lime phosphate bringing down the pepsine entangled with it. Pepsine 



1 Annalen der Chemie und Pharmacie, 1854, p. 42. 



2 Bernard. Le<;ons de Physiologic Exp6rimentale. Paris, 1856, p. 396. 



