26 
Book V. 
Fowls seem 
to form 
lime and 
phospho 
rus. 
ANIMAL FUNCTIONS. 
The phosphat of lime taken in was 136.509 gr. 
That given out was . ....... 274.305 gr. 
131766 
Consequently there must have been formed, by di 
gestion in this fowl, no less than 137.796 grains of 
phosphat of lime, besides 511.911 grains of carbonat. 
Consequently lime (and perhaps also phosphorus) is 
not a simple substance, but a compound, and formed of 
ingredients which exist in oat-seed, water, or air, the 
only substances to which the fowl had access. Silica 
may enter into its composition, as a part of the silica 
had disappeared; but if so, it must be combined with a 
great quantity of some other substance 
These consequences are too important to be admitted 
without a very rigorous examination. The experiment 
must be repeated frequently, and we must be absolutely 
certain that the hen has no access to any calcareous 
earth, and that she has not diminished in weight ; be 
cause in that case some of the calcareous earth, of which 
part of her body is composed, may have been employ 
ed. This rigour is the more necessary, as it seems 
pretty evident, from experiments made long ago, that 
some birds at least cannot produce eggs unless they have 
access to calcareous earth. Dr Fordyce found, that if 
the canary bird was not supplied with lime at the time 
of her laying, she frequently died, from her eggs not 
coming forward properly†. He divided a number 
of these birds at the time of their laying eggs into two 
parties : to the one he gave a piece of old mortar, which 
the little animals swallowed greedily; they laid their 
* Ann. de Cbim. xxix. 16. 
On Digestion, p. 25.