124 ELASTIC TISSUE. 
unless the tissue is investigated in a very young foetus, we can 
only detect cell-nuclei intermixed with fibres, or nuclei, in 
whose immediate proximity a small fasciculus of fibres arises 
on both sides. At an early stage of development the tendons 
have a gray appearance, not having assumed the white colour 
of the adult tissue. This fact is probably connected with 
a chemical difference existing between the young and perfectly 
developed fibrous tissue, as in areolar tissue. The quantity of 
the cytoblastema in which these cells are formed, and by which 
the fibres and tendons, when perfected, are probably connected 
together, must be extremely small, and cannot in any way be 
demonstrated by observation. Its existence can only be inferred 
by analogy with areolar tissue: it will be remembered that it 
was proved to be present in the foetal condition of that tissue. 
The quantity of cytoblastema, in comparison to the fibres pre- 
sent, seems to me to be the principal distinction between areolar 
and fibrous tissue in the adult. The fibrous tissue contains 
2 great many more fibres within a given space than the areolar 
does, and they are not more minute than those of the latter 
tissue. There is just as great a difference, however, between 
fibres of areolar tissue taken from different parts of the body, 
as there is between the ordinary fibres of tendons and the most 
common form of areolar tissue, so that a very gradual transi- 
tion takes place. 
8. Elastic Tissue. The distinction between elastic and 
fibrous tissue is exhibited at a very early period. But my 
investigations into the history of the development of this tissue 
are very incomplete, and extended only so far as to render 
it probable that it presented no exception to the principle of 
development from cells. I made use of the aorta of a foetal 
pig and the ligamentum nuche of a foetal sheep for the purpose. 
The tissue taken from these two parts was very different in its 
general character. In a pig’s embryo, of six inches in length, 
the aorta had already acquired its yellowish colour and perfect 
elasticity. The external coat could be easily drawn off in 
long pieces, almost, indeed, as a distinct tube. Having drawn 
off a small portion of the middle coat (which, in order to avoid 
any suspicion of epithelium being mixed with it, was so care- 
fully done, that the internal surface of the vessel remained 
ES a ee 
