THE PHYSIOLOGY OF DIGESTION. 231 



can easily accommodate itself to the elasticity of the other 

 investitures. The villous rugee diminish towards the duo- 

 denum ; and at the pylorus they unite with some muscular 

 fibres to form a valvular apparatus, which prevents the 

 return of the food. The villous portion of the stomach 

 secretes the gastric juice, and within it chymification is 

 performed ; a fact which is proved by ruminants, having 

 stomachs wholly cuticular, in which the digestive process 

 does not go forward ; and by many animals having entirely 

 villous stomachs, in all of which perfect digestion is accom- 

 plished. 



The stomach, as a secreting organ, is very plentifully 

 supplied with blood from gastric, splenic, and hepatic 

 trunks ; which, with the exception of their main branches, 

 proceed in a tortuous direction, to avoid distending the 

 organ ; and, in accordance with the same end, the gastric 

 veins w^hich return the blood possess no valves to impede 

 its progress towards the vena portse. The nerves are sup- 

 plied by means of the par vagum, or eighth pair, and like- 

 wise from the sympathetic nerve, or ganglionic system. 

 The par vagum endowing it with the necessary feeling, the 

 sympathetic giving to it organic life. 



THE PHYSIOLOGY OF DIGESTION. 



Digestion may be characterized as that power whereby 

 substances wdiich are received into an animal body lose their 

 own properties, and become endowed with those necessary 

 to support the constitution of the creature that imbibes 

 them. To restore the tone of parts, rest is required ; and 

 to repair waste, food becomes necessary ; while hunger 

 and thirst stimulate animals to take in solid and fluid 

 aliments. That the stomach is influenced by the blind 

 longings of inorganic life is proved by the fact, that the 

 mere mechanical distention of a draught of w^ater w^ill, for a 

 time, satisfy the sensation of hunger ; but simple distention, 

 not satisfying an instinctive desire, instead of affording relief, 

 it only adds to the general prostration : it is probably by its 

 distending properties that food taken partly invigorates long 

 before perfect chylification has taken place. This fact is how- 

 ever better established by no man having absolute power to 

 quicken or delay his desire for nourishment. The mere 



