L ITS DIGESTIVE POWER. 37 



hydrates excepting starch: cane-sugar, gum, vegetable mucus 

 (bassorin), and cellulose, remain unchanged in the saliva; it is only 

 in certain species of sugar, and after long-continued digestion at 

 a high temperature, that we observe the formation of lactic and 

 subsequently of butyric acid. 



The saliva exerts no action whatever on albuminous and 

 gelatigenous food; its utmost effect being to relax their tissues like 

 pure water, and thus to render them more accessible to the action 

 of the gastric juice. 



Wright thought he had convinced himself from numerous 

 experiments that flesh is softened and rendered tender in its tex- 

 ture much more rapidly when digested with saliva, than when it is 

 subjected to the action of water; he further concluded from these 

 and similar experiments, that the saliva contributes essentially to 

 the digestion of animal substances; but Jacubowitsch and Frerichs 

 have recently shown by their more accurate and well-tested expe- 

 riments, that this view is utterly erroneous. 



Bernard and Barreswil* believed that they were justified from 

 some of their experiments in laying down the following propo- 

 sition : " Le sue gastrique, le fluide pancreatique, et la salive, 

 renferment un meme principe organique, actif dans la digestion : 

 mais c'est seulement la nature de la reaction chimique, qui fait 

 differer le role physiologique de chacun de ces liquides, et qui deter- 

 mine leur aptitude digestive pour tel ou tel principe alimentaire." 



If this view had not been fully controverted by the admirable 

 experiments of Jacubowitsch and Frerichs, its untenability would 

 have been manifest to every one on a mere repetition of Bernard 

 and BarreswiPs experiments. 



Liebig has suggested that the saliva may be designed, from its 

 tendency to frothing, to convey atmospheric air into the stomach 

 and intestinal canal. Wright and others subsequently to him 

 have shown that starch is metamorphosed by saliva obtained by 

 expectoration, (which has consequently been sufficiently exposed 

 to the action of the air,) without further access of oxygen; and 

 Valentin t has very correctly stated that oxygen is not necessary 

 for the digestion of animal substances by the gastric juice facts 

 which have been advanced in refutation of Liebig's view ; but it 

 should be borne in mind that these experiments were not con- 

 ducted with such accuracy as to exclude all access of oxygen, and 

 that they cannot therefore be advanced as sufficient evidence 



* Compt. rend. T. 21, p. 88. 



t Lehrb. d. PhysioJ. des Mensclien. Bd. 1, S. 280. 



