314 Proceedings of Royal Society of Rdiiiburgli. . [may 7 , 
It is impossible to say, without most careful experiments and 
analyses, how, and in what proportions, these substances are found in 
the blood and lymph in hens ; although in the human subject 
numerous analyses have been made. As to the transformation of these 
lime salts into the carbonate, we should be tempted to explain it some- 
what as follows Even on microscopic examination it is evident, as 
above noted, that the secreting cells of the lower part of the oviduct 
are in a state of very great activity, not only those of the follicles, 
but also the slightly columnar cells of the superficial layer. The 
special function of these cells appears to be to secrete the lime from 
the salts brought to them by the blood and lymph. Tliis lime 
evidently accumulates in the epithelial cells, and is then thrown out 
on to the free surface, just as urate, oxalates of lime, soda, &c., are 
secreted by the renal epithelium. 
These secreting cells have apparently a further function, — that of 
separating the organic matter in which the lime is embedded in the 
form of minute granules. As in all active tissue changes, there is 
a certain disintegration of the cells, and certain wmste products are 
formed, even in the act of secreting or excreting other waste pro- 
ducts : urea (carbonate of ammonia '?) and carbonic acid gas are given 
off as the result of this activity of the epithelial cells in bringing 
the lime and organic matter to the surface 3 and the lime in a 
nascent condition, as it were, meeting with the carbonic acid in 
a similar condition, readily combines with it, and we have the car- 
bonate formed, it may be, in the cells themselves, or possibly on 
the surface of the secreting membrane. Sufficient carbonic acid gas 
is present in the oviduct, as in every other cavity and on every other 
surface of the body, to keep a portion of the lime in solution after 
it comes into the oviduct ; but in all probability part of the urea, 
being transformed into carbonate of ammonia, will increase the in- 
solubility of the carbonate of lime shortly after it finds its way into 
the oviduct. Such a theory is at any rate not without some sem- 
blance of probability. In support of it, it may be urged that, 
practically, the same thing takes place in the formation of bone, in 
which also we have an organic basis laid down by cells which, 
at the same time, actually secrete the salts of lime derived from the 
blood and lymph. Here, however, where the amount of phosphoric 
acid salts in the blood and lymph is large, and where there is no 
