IV, 2 — ly. 3. 95 



gall-bladder and' live long. But besides these there are other 

 animals that have no gall-bladder, though those old writers 

 were not aware of the fact, such as the carriel and the dolphin ;^''^ 

 and these also are, as it happens, long-lived. Seeing, indeed, 

 that the liver is not only useful, but absolutely necessary, to all 

 animals that have blood, it is but reasonable that on its character 

 should depend the length or the shortness of life. Nor less 

 reasonable is it that this organ and none other should have 

 such an excretion as the bile. For the heart, unable as it is to 

 stand any violent affection,'^ would be utterly intolerant of the 

 proximity of such a fluid ; and, as to the rest of the viscera, none 

 excepting the liver are necessary parts of an animal.'^ In con- 

 clusion, wherever we see bile we must take it to be residual or 

 excremental. For to suppose that it has . one character in this 

 part, another in that, would be as great an absurdity as to 

 suppose mucus or the dejections of the stomach to vary in 

 character according to locality and not to be excremental wherever 

 found. 



(Ch. 3.J So much then of the gaJl-bladder, and of the reasons 

 why some animals have one, while others have nbt.^ We have 

 next to speak of the mesentery and the omentum ; for these are 

 contained in the same cavity»as the parts already described. The 

 omentum, then, is a membrane containing fat ; the fat being suet 

 or lard according as the fat of the animaj generally is of the 

 former or latter description. What kinds of animals are so dis- 

 tinguished has been already set forth in an earlier part of this 

 treatise.^ This membrane, alike in animals that have a single and 

 in those that have a multiple stomach, grows from the middle of 

 that organ, along a line which is marked on it like a seam. Thus 

 attached, it covers the rest of the stomach and the greater part 

 of the bowels. It is found in all sanguineous animals whether 

 they live on land .or in water.^ Now the development of this 

 part into such a form as has been described is the result of 

 necessity. For, whenever solid and fluid are mixed together and 

 heated, the surface invariably becofnes membranous and skin-like.* 

 But the region in which the omentum lies is full of nutriment of 

 such a mixed character. Moreover, in consequence of the thick- 

 ness of the membrane, that portion of the sanguineous nutriment 

 will alone filter into it which is of a greasy character ; for this 

 portion is composed of the finest particles ; and when it has so 

 677b. 



