GOO FUNCTIONS OF ANIMALS. 



living animal, there is always a discharge of a liquid from the 

 villous extremities so abundant in that coat. This liquid, dis- 

 charged only when stimulating bodies are applied, or by the 

 stimulus of food, is, no doubt, the gastric juice, by the agency of 

 which the food is converted into chyme. It was shown decisive- 

 ly by the experiments of Dr Stevens, that this juice acts by dis- 

 solving the food, and that it produces the same effect upon food 

 out of the body, provided the temperature be kept at 100, as in 

 the stomach. 



Dr Beaumont of the United States army had an opportunity 

 of witnessing the process of digestion, and the appearance of the 

 gastric juice in the stomach of Alexis H. Martin, who had a per- 

 foration of the stomach, occasioned by a shot. The orifice gra- 

 dually healed ; but remained open with a kind of valve opening 

 from without, by means of which any thing could be introduced 

 into the stomach, and, by pushing the valve aside, the appearance 

 of the inner coat of the stomach and of the gastric juice could be 

 examined, and quantities of the gastric juice itself could be ex- 

 tracted, and its nature ascertained. The facts ascertained by Dr 

 Beaumont have been stated at considerable length in a preced- 

 ing chapter of this work, to which the reader is referred. 



The gastric juice, as observed by Dr Beaumont, was a pure, 

 limpid, colourless, slightly viscid fluid. It exhaled a weak odour, 

 not disagreeable, but slightly aromatic. Its taste was feebly sa- 

 line, and it always contained an uncombined acid, which Dr 

 Prout first showed to be the muriatic. The true gastric juice is 

 secreted only during digestion, and does not exist in the sto- 

 mach at any other time. What was taken for it by Spallanzani 

 and other experimenters towards the end of the eighteenth cen- 

 tury, was merely the saliva mixed with the mucus, secreted to lu- 

 bricate the stomach, and protect it from the action of certain sub- 

 stances sometimes present, which might otherwise injure it. 



From the experiments of Eberle, M tiller, and Schwann, for- 

 merly stated, it follows that the gastric juice contains also an- 

 other substance, called pepsin, some of the most remarkable pro- 

 perties of which have been detailed in a preceding chapter of this 

 work. It is by the united action of the muriatic or acetic acid 

 of the gastric juice, and of the pepsin which it contains, that the 

 food in the stomach is converted into chyme. 



When casein, gelatin, or gluten is put into water, acidulated 



