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Akt. XI. — Some Expei'hnents on the Changes which take 
jplace in the Fixed Principles of th e Egg during Incubation . 
By William Prout, M. D. F. R. S *. 
We place great confidence in every thing that comes from 
the pen of’ the author of the interesting memoir of which we 
are now to give an account. Dr Prout’s great accuracy, in- 
defatigable perseverance, and sound judgment, give to all his 
investigations the stamp of unalloyed excellence. The pre- 
sent memoir contains a series of experiments on a very curious 
and important subject ; and although, as Dr Prout remarks, 
“ the experiments are much less perfect than he could wish,” 
still they add greatly to our present knowledge, and give room 
for interesting physiological views. In the year 1816, Dr Prout 
commenced a series of experiments on the egg during incubation, 
with the view of ascertaining the nature of the changes which 
take place during that process. This inquiry was chiefly limited 
to the earthy and saline matters ; but his attention was parti- 
cularly directed to the source whence the earthy matter of the 
skeleton of the chick was derived. 
With these views, the egg was analysed in its recent and un- 
altered state, and at the end of the first, second, and third 
weeks of incubation. His experiments were chiefly confined 
to the eggs of the domestic fowl, but were likewise extended 
to those of the duck and turkey. This investigation, Dr Prout 
informs us, was renewed, and the following statement contains 
the results of his various experiments. 
Preliminary Experiments on the Egg in its recent and unal- 
tered State. 
The specific gravity of new laid eggs has been found to 
vary from 1.08 to 1.09. When kept for some time, eggs, as is 
well known, rapidly lose weight, and at length become so light 
as to swim in water. This diminution of specific gravity is pro- 
duced by the substitution of air for a portion of the water 
which escapes. The following table shews the gradual loss 
of weight of an egg, during a period of two years : 
* Abridged from Dr Prout’s Memoir in the Philosophical Transactions, 1S2£, 
Part II. 
