1888-89.] Mr Irvine & Dr Woodhead on Carbonate of Lime. 351 
cells are not epithelial in character, the matrix, though separate, is 
closely associated with the cells, especially during its formation, 
and the lime is deposited in the matrix, also apparently by a process 
of dialysis. 
Phosphoric acid combined with alkalies and alkaline earths is 
found in large and constant quantities in the blood and lymph. 
It acts as a carrier of lime, &c., to every point of the body where 
carbonic acid may be given off. Carbonate of lime is formed, and 
the phosphoric acid re-enters the circulation to continue its work 
as a carrier. 
The nascent carbonic acid given off by the cells in the neighbour- 
hood of the bone matrix, brings about precipitation of bath 
phosphate and carbonate of lime, which salts are dialysed into the 
matrix. In most of the secreting layers and in the fluids supplied 
to them, lime is found as some form of phosphate. Where the fluids 
bathe the matrix, or where there is no intervention of an epithelial 
secreting layer, the lime is thrown down very largely as phosphate 
as in bone, but where an epithelial secreting layer is found, or where 
there is much distance or tissue between the fluids and the seat of 
deposition, carbonate of lime preponderates. 
In the secreting layer of the mantle of certain molluscs, or in that 
of the oviduct in the hen, the lime in the epithelial cells is princi- 
pally phosphate, whilst the fluid bathing its outer surface and the 
shells themselves contain the lime, principally, in the form of a 
carbonate. If there is a definite interval between the secreting 
surface and the area of deposition, or if much chitin or other tissue 
is developed between the actively secreting cells and the tissue in 
which the lime is deposited, there is always a greater tendency to 
the formation and deposition of carbonate of lime. 
Lime salts, of whatever form, are deposited only in vitally inactive 
tissue. They are found in bone matrix, in chitin, in old fibrous 
tissue (?), or in tissues that have undergone fatty or caseous degener- 
ation. Wherever such dead tissue is found, dialysis goes on, and 
lime in an insoluble condition is deposited. 
Although the lime is deposited in dead tissue and dialysed through 
a vitally inactive membrane, it is apparently separated from the 
fluids of the body through the activity of carbonic acid secreting 
protoplasm of cells. 
