542 
OSSIFICATION OF THE AORTA. 
It is to these unnatural ossific deposits and that are connected 
with disease, that I now wish to call your attention. Ossifi- 
‘ cation, whether on external or internal parts, appears to be 
commenced, carried on, and perfected, by the same process. 
Let us consider, as briefly as possible, what this process is. The 
first step which nature takes, is in causing the arteries to pour 
out a sort of jelly. Into the centre of this, an artery is soon 
seen running; other arteries appear, and form a net-work around 
and in it. These vessels are at first transparent; but they soon 
begin to dilate, and, whenever the red-coloured blood begins to 
appear, then ossification quickly succeeds, the arteries being so 
far enlarged as to carry the coarser parts of the blood. A centre 
of ossification now begins to appear in this jelly ; other points are 
successively formed : complete ossification follows, and buries and 
hides those vessels by which it was formed. 
It is also to be observed, that this process is quickly perfected, 
and that it goes on without inflammation being present; for we 
have heard of ossification of the lungs and liver to a considerable 
extent without its being suspected, during life, that any thing was 
wrong with those parts. 
But it appears that ossification is often consequent upon 
inflammation, as, in the example of splents. We often have 
horses brought to us with swelling and inflammation where 
a splent occurs, which feels as if it contained coagulable lymph ; 
by and by it becomes harder, and at last bone. 
Having, therefore, shewn that the formation of bone, natural 
or unnatural, external or internal, is brought about by the same 
process, and believing that it may take place with or without 
any previous inflammation, I proceed, in the second place, to 
give some particulars relative to the casein question. 
In the month of May last a horse of our own, which we had 
driven in harness many years, was destroyed, on account of 
being lame from the navicular disease. He had not been a 
healthy horse for some time : after a day’s journey, he was quite 
done up, affected with loss of appetite and weakness in his loins, 
which would occasion him to drop; and sometimes there was 
difficulty in retaining his urine : he had been turned out to grass 
for twelve months, but had not got into condition by it. 
On a post-mortem examination, I found a mass of scirrhous 
deposit attached to the aorta, and the coats of that vessel com- 
pletely ossifiediov several inches, just where the renal arteries are 
given off. The coats of the renal arteries were much thickened, 
and their elasticity quite destroyed ; and both the lungs and liver 
had small spiculae of bone in their substance. This extraordinary 
process must have been going on for some time, yet its existence 
was not suspected. 
