1888-89.] Mr Irvine & Dr Woodhead on Carbonate of Lime. 325 
various salts of lime being added to the food of the hens, and we 
found that the shells of the eggs laid by them, thus fed, invariably 
consisted of carbonate of lime, always in the same proportion, 
practically, as found in normal egg shells, mere traces of phosphate 
and sulphate of lime being present. 
We found that (unless when carbonate of lime itself was given) we 
obtained the most favourable results with phosphate of lime, which 
was added to the food with the same precautions as already 
described, and seemingly the fowls had no difficulty in assimilating 
this salt, and producing from it eggs with normal shells, thus 
bearing out the view we hazarded in our former paper that the 
lime is carried to the secreting surfaces of the duct as phosphate 
of lime and soda. It would thus appear that lime salts, in whatever 
condition they are absorbed, are during the digestive processes 
converted into phosphate, and carried as that salt to the secreting 
surfaces in the oviduct, at which point it probably meets with, and 
is decomposed by, nascent or combined carbonic acid ; at the same 
time, structureless or amorphous carbonate of lime is elaborated, 
possibly in combination with protoplasmic matter.* 
Before concluding this portion of the paper it will be interesting 
to note the observations made with a view to determine whether 
birds can produce shells from salts of the metals having analogous 
properties to those of calcium. Compounds of strontium and 
magnesium were, under the conditions already fixed, administered 
to the laying hens. Salts of barium could not be employed on 
account of their poisonous nature. The result invariably was that 
* A most interesting observation on the changes through which the lime 
salts may go, is that afforded by the transference of lime from the shell of the 
chick’s egg (Lehmann, Physiological Chemistry, vol. i. p. 417), where it is found 
as the carbonate, to the yolk and developing chick embryo, where it appears 
in the form of the phosphate. Prout, Phil. Trans., 1822, p. 365, pointed 
out further, that the amount of phosphorus in the yolk remains constant 
throughout the whole course of development of the chick, but that there is a 
steady and continuous increase in the amount of lime ; and Lehmann argues 
that, as the egg shell becomes both lighter and more brittle, the lime is derived 
not from without, as Prout suggested, but directly from the shell. He says, 
“The phosphorus exists chiefly in the yolk, where it occurs as glycero- 
phosphoric acid, which during incubation is gradually decomposed, so that 
the liberated phosphoric acid unites with the lime which passes over by 
endosmosis from the shell into the egg to form this salt.” It is evident from 
this that dialysis plays an important part in the process of lime distribution 
from the egg shell and its membrane to the growing embryo. 
