PARTS OF ANIMALS, II. v.-vi. 



heat. The same cause is responsible for the com- 

 parative sterility of fat animals : that part of the 

 blood which ought to go to form semen and seed gets 

 used up in forming lard and suet, which are formed 

 by the concoction of blood. Hence in fat animals 

 there is either no residue " at all, or else very little. 



I have now spoken of blood, serum, lard and suet, 

 describing the nature and the Causes of each of them. 



VI. Marrow, again, is really a form of blood, and not, Jrarrow. 

 as some^ think, the same as the seminal substance'' 

 of the seed. This is proved by the case of very young 

 animals. In the embryo, the parts are composed out 

 of blood and its nourishment is blood ; so it is not 

 surprising that the marrow in the bones has a blood- 

 like appearance. As they grow and become mature,^ 

 the marrow changes its colour just like the other parts ^ 

 of the body and the viscera, which while the creature 

 is young all have a blood-like appearance owing to the 

 large quantity of blood in them. 



Animals which contain lard have greasy marrow, 

 like lard ; those whose concocted blood produces not 

 a substance like lard but suet have suety marrow. 

 Hence, in the horned animals which have teeth in 

 one jaw only the marrow is suety, and in the animals 

 that have teeth in both jaws and are polydactylous it 

 is like lard. (The spinal marrow cannot possibly be 

 of this nature because it has to be continuous and 

 to pass without a break right through the whole 

 spine which is divided into separate vertebrae ; and if 

 it were fatty or suety it could not hold together as 

 well as it does, but it would be either brittle or fluid.) 



" Dynamis. See Introduction, pp. 30 if. and note on 646 a 14. 



^ Lit. " are concocted." 



• A good instance of Aristotle's usage of the term " part." 



14'5 



