PHYSIOLOGY. 



they occur successively in the different stages through which the 

 matters pass. 



CCII. Animals are determined to take in aliment by the 

 appetites of hunger and thirst. 



CCIII. Hunger is an appetite depending upon a sensation 

 referred to the stomach, and arising from a particular state 

 of it. 



This state seems to be, in some respect, the degree of empti- 

 ness, but, more especially, the state of contraction in the mus- 

 cular fibres which emptiness gives occasion to. This state of 

 contraction may also be excited by certain stimulants applied ; 

 but, more commonly, it depends upon, and is correspondent to 

 the state of inanition, and therefore of contraction in the ves- 

 sels of the skin emitting the matter of perspiration. " I have 

 here advanced an opinion which I believe to be new ; and I 

 will, therefore, allow you to receive it with such diffidence as 

 you think proper ; but I must observe that I find it necessary 

 to have recourse to this opinion, because the ordinary accounts 

 are not at all satisfactory. Haller supposes that the uneasy sen- 

 sation of hunger is owing to the application of the opposite sides 

 of the stomach to each other, and to the friction, or mutual at- 

 trition hence arising. But I doubt if ever the opposite sides of 

 the stomach come to be applied to one another, so as to be ex- 

 posed to any such friction or attrition. From every view of 

 the stomach, in its natural state, it appears that its muscular 

 fibres contract in such a manner as still to preserve the cir- 

 cular form of the stomach, and that the two opposite sides never 

 fall flat on each other but are always kept at some distance. 

 In men killed by long fasting, the stomach, instead of being a 

 large bag, has been found of a small size, but still retaining its 

 circular form ; so that no attrition could be produced. More- 

 over, in that state of the stomach no peristaltic motion is going 

 on, nor will the alternate pressure of the diaphragm, which 

 moves the whole stomach, produce any attrition of its sides. 

 Further, I say this friction could only take place between two 

 dry surfaces, but this can never occur in the stomach, which is 

 still filled in proportion to its capacity with a considerable quan- 

 tity of mucus, some of the relics of food, and the gastric fluid, 

 which will prevent any friction. 



