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MESSRS. J. TOMES AND C. DE MORGAN ON THE 
only of the same action. Hence a more particular examination of the cellular mass, 
by which bone appears to be absorbed in the one case and deposited in the other, 
naturally suggests itself, and attention has been directed to this point as frequently 
as favourable opportunities for observation have presented themselves. The differ- 
ences, how'ever, in microscopic characters between the two tissues, have not been so 
strongly marked, as to admit of any definite description being given, by which the 
one may, in all instances, be distinguished from the other, when removed from their 
natural positions, as is almost necessarily the case with regard to the absoibent cells, 
from the readiness with which they separate from the wasting bone (Plate IX. 
figs. 27 and 34). 
Lacunal cells moreover will not be found in the absorbing tissue ; but it is not easy 
to recognize them, even in the tissue from which bone is developing, as the\ aie 
frequently obscured by the osteal cells ; so that their presence, although a good 
ground of distinction, cannot in all instances be demonstrated. When, how^ever, 
developmental cells are seen in situ, their character is readily distinguished. They 
are closely applied to the surface of the increasing bone, which loses the festooned 
and assumes an even outline, to which the osteal cells adhere. 
The source from which the cells destined for effecting absorption arise is at present 
unknown to the authors, any further than that they arise in connection with sott 
tissues, the three situations in which they occur being beneath the periosteum or 
medullary membrane, or within an Haversian canal. These are no doubt the points 
from which the development of the ceils starts, but the law which regulates theii 
occurrence at one part rather than another, and gives to them their peculiai function, 
is, at present unexplained. Neither is it more easy to understand why, at a paiti- 
cular period, the process of absorption is arrested and development of new tissue com- 
mences ; the new bone may, for anything we have seen to the contrary, be formed fiom 
the same cells that have been concerned in the removal of the old. The organ by 
which the fangs of teeth are absorbed offers a very favourable object for examination. 
This we find to commence within or beneath the periosteum which covers the fang 
of the tooth, and increases with the wasting of the tooth, until it comes in contact 
with the pulp, which then assumes a similar function and becomes an absorbing 
organ, increasing gradually in size, till, if the tooth be left undisturbed, but little of 
the crown remains excepting the enamel. If, when in this condition, the crown of 
the tooth be carefully removed, we shall see the absorbent papillae projecting a little 
above the gum, firm in substance, and not disposed to bleed unless rudely handled. 
Within two or three days it becomes covered with epithelium, either by the exten- 
sion of the epithelial membrane from the surrounding parts, or from a change in 
character in the superficial ceils of the part itself*. Gradually the papilla loses its 
* In the 26th volume of the Medico-Chirurgical Transactions, there is a short paper by Mr. Dalrymple, 
in which he describes a small tumour from the eyelid, consisting essentially of epithelial cells, in which the 
ordinary contents had been replaced by ossific matter. 
