398 Dr. Prout’s experiments on the changes which take place 
on the uses of the yelk, and the apparent generation of earthy 
matter. 
Sir Everard Home and Mr. Hatchett have concluded, 
from their experiments, that the yelk is analogous to the 
milk of viviparous aimals, but more concentrated, and that 
its chief use is to afford a pabulum to the young animal 
during incubation.* This opinion, which is indeed as old as 
Aristotle, - f is corroborated in a striking manner by the 
present inquiry. Mr. Hatchett has also made the im- 
portant and curious remark, that in the ova of those tribes 
of animals, the embryos of which have bones, there is a por- 
tion of oily matter ; and in those ova whose embryos consist 
entirely of soft parts, there is none. Hence it is concluded, 
that a certain portion of oil is necessary for the formation of 
bone. The present inquiry cannot be said to confirm, or 
invalidate, this remark, for although in the earlier stages of 
incubation, before ossification has commenced, a portion of the 
oil of the yelk is appropriated to the purposes of the economy 
of the animal, yet by far the greater portion of it remains ; 
and some of it is even retained by the yelk till its final dis- 
appearance.^ One great use of the yelk evidently is to fur- 
• Philos. Trans. Vol. 106, p. 301, et seq. 
f 'H fxev ovv apxh toD veorrou gjnv ex tou AeujcoO, rj Ss Tgocpr) tov o/x^«AoD ex row 
Aristotelis de Animal. Hist. VI. 3. (Ed. Schneider.) Pliny makes the 
same remark. Ipsum animal ex albo liquore ovi corporatur. Cibus in luteo est. 
Hist. Nat. X. 53. 
X I examined a chick on the 18th day after incubation. The yelk was now re- 
duced to less than 2 grains, but it was of its original yellow colour, and of course 
contained oily matter. When burnt, it left traces of phosphate of lime. Dr. 
Macartney attempts to show that the yelk does not pass into the intestine 
through the ductus vitello intestinalis, but is taken up by absorption ; and an 
argument he adduces in support of this opinion, is, that the earthy matter is left 
