1888-89.] Mr Irvine & Dr Woodhead on Carbonate of Lime. 343 
fication of the fattily degenerated material. On careful examina- 
tion of such a patch it will be found that, during the earlier stage 
of calcification, there is always a quantity of fibrous-looking tissue 
around the calcifying area. Eventually even this becomes calcified, 
often without the intervention of any regular fatty degeneration. 
Here all the conditions for dialysis are extremely favourable ; 
there is first the dead tissue in close proximity to a blood-stream, 
but cut off from it, and from the lymph both from within and from 
the small vasa vasorum by a layer of fibrous or formed tissue, which, 
in the first instance, acts as a dialysing membrane between the 
lymph and the dead matter, and then as a medium in which more 
lime may be deposited. All pathologists are acquainted with the 
similar changes that take place in the middle coats of the medium- 
sized vessels of old people, in old unabsorbed infarctions, especially 
of the spleen, in the walls of old encysted trichina spiralis, in 
extra-uterine foetus formation, especially in the superficial parts, 
in caseous infiltrations of the peri- or epicardium, on the pleura in 
old people, and in caseous tubercular masses in the lung, and in 
softening glands in the human subject, and especially in the 
Herbivora.* 
If we take the last as an example, we find that we have another 
factor present, of which mention has already been made in connection 
with bone, i.e., rapid new cell-formation in the immediate neighbour- 
hood of the dialysing membrane, which in this instance consists 
of the fibrous layer immediately surrounding the caseous tissue. 
Here then are the three factors necessary : — tissue thoroughly de- 
vitalised, where we have dead albumenoid matter; secondly, there 
is around the mass of dead tissue, a layer of formed material 
as fibrous tissue, which, as in the case of bone or cartilage matrix, 
may form a dialysing membrane ; and, lastly, there is the layer of 
proliferating cells always found in the region of any foreign or 
dead mass, which may, in such, a case, be said to take the place of 
osteoblasts of bony tissue, as generators of, amongst other things, 
carbonic acid. On careful examination of a gland from a tuberculous 
cow, in which caseation was almost complete, but in which 
* (See Ziegler’s Pathology ; translated by Macalister, vol. i. pp. 96, 97 ; 
Litten, Der Hwmorrhagische Infarct ., 1879; Kyber, Virch. Archiv, vol. lxxxi. ; 
Payne, Pathology , p. 198 ; Coat’s Pathology , p. 127.) 
