Pepper. ] 36 {Dec. 2, 1870. 
pearances contradict any such supposition, and clearly show that while 
in the cancellated and imperfectly compact tissue of the original shaft a 
process of rarefaction (osteoporosis) has been advancing by atrophy of 
the bony lamelle, there has also been an active process of periostitis re- 
sulting in the formation of thick layers of new bone on the exterior. 
Another means of distinguishing the line of demarcation between the 
original shafts and the new-formed layers, is the abrupt change in the 
direction of the cancelli already referred to. 
It isevident, also, that the periostitis has not been uniformly continuous, 
but that for a variable time its intensity was such that the inflammatory 
product was capable of but imperfect ossification, and remained as cancel- 
lous tissue ; while at irregular intervals thin layers of imperfectly com- 
pact tissue have been formed. The occurrence of this long standing, but 
not uniform process of periostitis ossificans appears to account, in every 
instance, for the changes observed on the exterior of the original shafts. 
In addition to this uniform hyperostosis, it will be observed from the de- 
scription (see pp. 23, 24) that the same process of periostitis has given rise 
to varied forms of porous osteophytes. 
3. In some places, however, it is evident that a still further change has 
occurred, consisting in the gradual conversion of the cancellous tissue 
into compact bone. This process of consecutive or secondary induration 
is most marked in the layers of bone formed by the periosteum ; though 
it is present in the shafts of the tibie, femora and some other bones. It 
is manifestly impossible to determine accurately the portions which 
have been rendered compact by this process, but the disposition of the 
successive layers of new-formed bone is, in general, so much like that 
above described, that we are inclined to regard all the areas of compact 
bone of any considerable thickness as due to this secondary change. 
It would, indeed, appear but probable that as the high degree of inflam- 
mation, under which the layer of cancellous tissue had been formed, sub- 
sided, there should be a tendency to the formation of successive layers of 
bone on the interior of the walls of the cancelli. It is especially in con- 
nection with this point that the result of the microscopical examination 
of the sub-periosteal layers is of so much interest. It will be observed 
(see Fig. A) that in the newly-formed compact bony tissue, the lamella 
are arranged concentrically around the vascular canals; a mode of ar- 
rangement which strongly points to the occurrence of the process of con- 
secutive induration, as we have above described. 
The specimens are deposited in the Museum of the College of Physi- 
cians. 
J. EWING MEARS, M. D. 
WM. W. KEEN, M. D. 
HARRISON ALLEN, M. D. 
WM. PHP PER, Mi D. 
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