346 Proceedings of Royal Society of Edinburgh. [sess. 
The importance of this difference in the constitution of the urinary 
salts should he appreciated by clinicians. 
To return to the examples of calcification. Another, bearing 
upon the point in question, is the calcification going on in the super- 
ficial layers of tissue of the new growth in a case of extra-uterine 
fcetation. Here, again, we have the dead matter in the centre 
surrounded by a layer of fibrous tissue and again by a granula- 
tion tissue layer. The calcification appears first in the superficial 
dead tissues immediately beneath the fibrous layer. The same 
thing occurs in the membranous cyst of the old trichina spiralis. 
In the uterine fibroid the centres of calcification are numerous, 
at first small, but they gradually run together; their method of 
formation appears to differ from any that we have examined in 
other positions, but even in them, the evidence is not at all against 
the theory of dialysis into the dead tissue. In connection with 
this process of calcification our attention was drawn by Mr H. A. 
Thomson, M.B., to the peculiar solid wedge-shape “infarcts” 
found near the ends of tuberculous bones. Konig describes them 
as probably the result of a cutting off of the blood supply from a 
small wedge-shaped area, as in any other example of infarction. 
Numerous objections have been taken to this explanation, and the 
masses have been said to be due to the formation of tubercular 
sequestra. In all probability both processes enter into the causa- 
tion of these pale hard masses. Owing to the tuberculous changes 
in and around the vessels, in such a case there is formed an infarcted 
area. This is borne out by recent experiments by Klein, Watson, 
Cheyne, and others. But beyond this, the infarcted area, there may 
or may not be a primary tubercular process. Even when there is 
no primary tubercle the osteoblasts and other cells first proliferate 
and then die in situ; they, then, as in other positions, become 
swollen and hyaline, and are then rapidly infiltrated with lime salts, 
and the infarcted bone assumes a much denser appearance than the 
normal bone surrounding it. It is conceivable that the lime salts in 
such a dense compact tissue can only come by some more or less 
mechanical process such as we have described. A similar condition 
occurs in certain diseases of bone, especially during the later 
stages of osteo-sclerosis where that condition is associated with 
specific disease. The conditions are the same in all cases,-— dead 
