ON GENERATION. 213 



is of a yellow colour, in another of a tint between white and 

 yellow ; it is quite round, of variable size, according to the size of 

 the bird that lays the egg, and, according to Aristotle, of a 

 deeper yellow in water birds, of a paler hue in land birds." 

 The same author 1 also maintains that "the yellow and the white 

 of an egg are of opposite natures, not only in colour but in 

 qualities; for the yellow is inspissated by cold, which the white 

 is not, but is rather rendered more liquid; and the white, on 

 the contrary, is thickened by heat, which the yellow is not, 

 unless it be burned or over-done, and it is more hardened and 

 dried by boiling than by roasting." As in the macrocosm the 

 earth is placed in the centre, and is surrounded by the water 

 and the air, so is the yelk, the more earthy part of the egg, 

 surrounded by two albuminous layers, one thicker, another 

 thinner. And, indeed, Aristotle 2 says that, "if we put a 

 number of yelks and whites together, and mix them in a pan, 

 and then boil them with a slow and gentle fire, that the whole 

 of the yelks will set into a globular mass in the middle, and 

 appear surrounded by the whites." But many physicians have 

 been of opinion that the white was the colder portion of the 

 egg. Of these matters, however, more by and by. 



The chalazse, the treads or treadles (gralladura Ital.) are two 

 in number in each egg, one in the blunt, another in the sharp 

 end. The larger portion of them is contained in the white ; 

 but they are most intimately connected with the yelk, and with 

 its membrane. They are two long-shaped bodies, firmer than 

 the albumen and whiter ; knotty, not without a certain trans- 

 parency like hail, whence their name ; each chalaza, in fact, is 

 made up of several hailstones, as it seems, connected by means 

 of albumen. One of them is larger than the other, and this 

 extends from the yelk towards the blunt end of the egg ; the 

 other and smaller chalaza stretches from the yelk towards the 

 sharp end of the egg. The larger is made up of two or three 

 knots or seeming hailstones, at a trifling distance from one 

 another, and of successively smaller size. 



The chalazse are found in the eggs of all birds, and in 

 wind and unprolific as well as in perfect or prolific eggs, duly 

 disposed in both their extremities. Whence the supposition 



1 Hist. Anim. lib. vi, cap. 2. 2 Hist. Anim. et De Gen. Anim. lib. iii, c. 1. 



