156 FUNCTIONS OF NUTRITION. 



gastric juice does not convert cane-sugar into glucose at a boiling- 

 temperature as hydrochloric acid would do.* It is acknowledged 

 that both the acids in question may be obtained from gastric juice 

 by distillation and analysis ; f but it is considered doubtful whether 

 the 'hydrochloric may not be liberated by decomposition, or the lactic 

 produced by fermentation, during the process. Finally, Richet J has 

 investigated the subject by a method which avoids prolonged chemical 

 manipulation. This method depends on the comparative solubility in 

 ether of organic and mineral acids. The organic acids are readily 

 soluble in this menstruum, and ten volumes of ether, shaken up with 

 one volume of a watery solution, will remove from it one-half the lactic 

 acid which it contains. The mineral acids, on the other hand, are but 

 slightly soluble in the same fluid ; and it requires 500 volumes of ether 

 to extract from a watery solution one-half its acid ingredient, should 

 this be hydrochloric acid. From experiments of this kind the author 

 concludes that the fresh gastric juice, unmixed with food, contains 

 almost exclusively hydrochloric acid ; the proportion being not more 

 than one part of lactic acid to twenty parts of hydrochloric ; but that 

 if kept for some days the organic acid may so increase as to prepon- 

 derate over the mineral ; and furthermore, that gastric juice, if mixed 

 with food, may form organic acids during digestion to the amount of 

 one-third or one-half the mineral acid present. The subject, therefore, 

 is not altogether free from obscurity. 



It is certain, however, that the normal free acid of the gastric juice, 

 if neutralized, may be replaced by either lactic or hydrochloric acid 

 without impairing its digestive properties. Other acid bodies, both 

 mineral and organic, as dilute sulphuric, nitric, or acetic acids are 

 also available for the purpose, though much less so than the fore- 

 going ; while phosphoric, oxalic, and tartaric acids, according to Leh- 

 mann, are nearly inert in this respect. 



I The remaining characteristic ingredient of the gastric juice is its 

 albumenoid matter, known under the name of pepsine. This is the 

 special ferment produced by the gastric follicles, to which the peculiar 

 digestive properties of the secretion are due. It is precipitable from 

 the gastric juice by alcohol in excess, and after precipitation may be 

 redissolvcd in water with its qualities unchanged. Gastric juice is 

 essentially an acidulated solution of pepsine. Both the ferment and 

 the acid must be present in order that the secretion may exert its 

 digestive power. If fresh gastric juice be neutralized by the addi- 

 tion of an alkali or alkaline carbonate, it becomes inactive notwith- 

 standing the presence of pepsine ; but its activity may be restored by 

 acidulation. On the other hand, gastric juice from which the pepsine 

 has been thrown down, or in which it has been rendered inactive by 

 boiling, has no digestive power although its acidity remains. 



* Revue des Sciences Medicales. Paris, 1878, tome xii., p. 715. 

 fHoppe-Seyler. Physiologische Cheraie. Berlin, 1878, p. 215. 

 JComptes Kendus de 1' Academic des Sciences. Paris, 1877, tome Ixxxiv., p. 1514. 



