146 PHYSIOLOGY 



It is hard to determine what is the true shape of the stomach while 

 in the living body, as it takes on different shapes in proportion to the 

 fullness of it and different pressures ; but it will always have a ten- 

 dency towards that which it takes when inflated. Stomachs cannot be 

 divided according to the food which animals eat, because the shape in 

 many, whose food is very different, is nearly the same. 



In all quadrupeds, as far as I know, the stomach is shorter and 

 thicker than in the human, and does not become so gradually smaller 

 towards the pylorus. 



Of Digestion. 



Digestion is a process that is similar to no other process in nature : if 

 it was in any way similar to the natural changes that animal substances 

 alone, vegetable substances alone, or where both substances mixed, 

 undergo when left to themselves — I say, if it were so, then — digestion 

 would be equally good in all animals and in all people. But it is so 

 unlike these natural changes, that in all bad digestions these natural 

 changes are in a small degree allowed to take place. Digestion depends 

 upon a principle that belongs to the containing, and not to the con- 

 tained, parts. 



The [power of the] containing [organ] may, and does depend on the 

 disposition of the body and mind, not so much on the constitution or 

 strength of the body ; for many weak constitutions have vast power of 

 digestion, and others the reverse. Its effects are immediate on dead 

 substances ; almost as quick as the effects of an acid on an alkali. Its 

 power depends upon life ; for, as soon as life is gone, even in the most 

 healthy, this power is lost, excepting what may be going on [at the time 

 of death], which continues for a little time. It depends on a living 

 principle in itself ; but that which is to be digested must be dead, or 

 have lost this living principle, or it cannot be dissolved. 



Like all other fermentations, it cannot act upon any living principle, 

 either animal or vegetable ; that principle must be first lost before any 

 change can be produced. If it was possible for an animal to live in 

 the stomach of another animal, supposing digestion not to be going on 

 in that stomach, it would then hive while digestion was going on ; for 

 that animal would not be in the least dissolved, because the living prin- 

 ciple in the animal would prevent or counteract the digestive quality of 

 the stomach. If this was not the case, then we might readily suppose 

 that even though the animal life was not immediately affected by the 

 digestive power, yet at last it might be destroyed by the external and 

 extreme parts of the animal being digested, and so the animal be obliged 

 to die, like a person with a mortification. But that a living animal 



