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Proceedings of Royal Society of Edinburgh. [sess. 
cannot with certainty isolate the compound, or, as yet, do more than 
indicate its composition, there is sufficient evidence that the 
changes we have indicated may occur through the instrumentality 
of such a compound. 
The same thing may he said in regard to the association of 
carbonic acid (as alkaline carbonates) with albumen, both acids 
being always present in the blood of animals in varying quantities, 
and, as asserted by Liebig, the proportion of these acids may vary 
to almost any limits, without altering the general character of the 
blood. 
Thus we have, without disturbance to its general characteristics, 
two distinct conditions existing in the blood of animals, and these 
conditions, in addition to those already mentioned, may, and doubt- 
less do, account, to some extent, for the secretion of lime salts in the 
different forms in which we find them to occur — in the one case the 
secretion taking the form of phosphates as in bone, and in the other 
that of carbonate of lime, as in shell and coral formation. 
In other words, when alkaline phosphates associated with lime 
and albumen preponderate in the blood, the lime is secreted in the 
form of phosphate, as in bone formation, so when the alkaline 
phosphates are partially replaced by an excess of alkaline car- 
bonates, as in marine animals, the lime is secreted principally as 
carbonate. 
In neither case are the lime compounds deposited in a pure form, 
as when the phosphate predominates it is always accompanied by 
a certain amount of carbonate, so when the carbonate predominates, 
phosphate of lime is always present as we found them in bone, and 
shell, and coral formation. It may be assumed in the one case that 
the albumen becomes converted into gelatine, which forms the 
structure in which the phosphate of lime is deposited in bone, and 
in the other into a chitinous mass in which the carbonate is deposited 
as in the exo-skeleton of crustaceans or the shell of the egg. 
These views are founded upon actual experimental results, for if 
a solution of alkaline phosphates and soluble lime salts in carbonic 
acid is allowed to stand for a short time, the clear solution soon 
becomes cloudy, and a precipitate is formed which is found to 
consist of phosphate of lime, and the same thing happens with a 
solution of alkaline carbonates and soluble lime salts in carbonic 
