GENERATION OF ANIMALS, III. ii. 



becomes fluid when it is concocted in the earth or by 

 means of incubation," and in that condition it becomes 

 nourishment for the animals that are taking shape. 

 When subjected to fire, or roasted, it does not become 

 hard, because it is by its nature earthy in the same 

 way that wax is ; and that is the reason why, when 

 eggs are overheated, [unless they are from a liquid 

 residue] ^ they become serous, and turn rotten (puria). 

 The white, on the other hand, does not congeal as a 

 result of frost, but tends rather to become fluid (I 

 have given the reason earlier) ; and when subjected 

 to fire, it becomes solid. This is why, when it is 

 concocted in connexion with the generation of the 

 young animals, it thickens ; for it is the white out of 

 which the animal forms and develops, while the yolk 

 becomes nourishment for it, and is the source from 

 which the parts as they are formed at the various 

 stages derive their growth. That, too, is why the 

 yolk and the white are kept distinct and separate 

 from each other by membranes, as having a different 

 nature from each other. For an exact account of how 

 these stand to one another both at the beginning of 

 the process of generation and during the process of 

 the young animals' formation, also for an account 

 of the membranes and umbilical cords, what is \^Titten 

 in the Researches '' should be studied ; for our present 

 inquiry it is sufficient that thus much should be clear, 

 viz., that once the heart has been formed (this comes 

 first of all) and the Great Blood-vessel has been 

 marked off from it, two umbiUcal cords extend from 



heated, it becomes soft ; and so when it is subjected to fluid, 

 it turns rotten owing to the excess of fluidity " (c/. 753 a 34, 

 above). 



* H.A, 561 a 3 — 562 b 2 ; but the description there is no 

 fuUer. 



293 



