38 SALIVA. 



against the accuracy of Liebig's view : there are, moreover, as we 

 know, certain processes, as for instance the vinous fermentation, in 

 which it requires the greatest exactitude of observation to demon- 

 strate the necessity of a slight access of oxygen. Then again, the 

 fact that only mixed saliva, that is to say, saliva which has been in 

 contact with atmospheric air, is capable of metamorphosing starch, 

 speaks rather in favour of Liebig's view than against it. Even if 

 the oxygen, which undoubtedly passes into the primes vies with 

 the saliva, exerts no effect upon the process of digestion in the 

 stomach, the use of this gas in the intestinal canal may readily 

 be understood, although it cannot be specially demonstrated. We 

 know that gases are present in the intestinal canal, and that these 

 gases are rich in carbonic acid and often also in hydrogen com- 

 pounds. The formation of the latter, whose passage into the blood 

 would be followed by very injurious results, must necesssarily be 

 greatly limited by the presence of free oxygen. According tq 

 the laws of the diffusion of gases, the presence of oxygen in the 

 .mtestines must diminish the withdrawal of oxygen from the blood 

 and the supply of carbonic acid and hydrogen to that fluid. 



Wright considers that one of the most prominent functions 

 of the saliva is its supposed property of serving as a necessary 

 stimulant to the stomach, and thus promoting the digestive process. 

 We have already frequently expressed our dissent from the dyna- 

 mical explanation of physiological phenomena; according to our 

 view, even the nerves cannot act independently of chemical changes, 

 and if we are to admit the control of dynamical forces on the 

 nervous system, we must first establish the existence of definite 

 chemical relations in proof of such an action. It appears to us 

 altogether inconsistent to attach any importance in physiological 

 chemistry to the obscure idea of an irritant. When I intro- 

 duced fresh saliva, through a fistulous opening, into the stomach of 

 a dog, I observed that the same amount of gastric juice was 

 secreted as when other mucous fluids were conveyed into the 

 stomach. There is no indication of any special irritant in ex- 

 periments of this kind ; and the stimulating action of the saliva 

 can hardly be required for the process of gastric digestion, since 

 solid substances, and more especially nitrogenous food, induce a 

 far more abundant secretion of gastric juice than pure saliva. 



Wright introduced from 3 to 10 ounces of saliva, through an 

 elastic-gum catheter, into the stomachs of dogs that had been kept 

 fasting, and observed, after the lapse of ten minutes, contraction 

 of the abdominal muscles, uneasiness, eructations, and vomiting. 



