26 
CiACCiOj on the Distribution of 
demonstrated by the use of certain reagents. This view 
seems to me to be strongly corroborated by the manner in 
which the pale fibres and the dark-bordered ones near the point, 
where they appear to cease, comport themselves with diluted 
acetic acid and concentrated sulphuric acid. Indeed, diluted 
acetic acid causes on the former as well as on the latter a 
granular appearance, with this difference only, that the 
granules in the pale fibres are smaller than in the dark- 
bordered fibres, but both kinds of granules refract light in 
the same way. On treating afterwards with concentrated sul- 
phuric acid the pale fibres which have been thus acted upon 
by acetic acid, the granules disappear, and the fine nerve- 
fibres remain as transparent tubes with faint outlines. It is 
plain, therefore, that concentrated sulphuric acid acts only 
upon the granules produced by the action of acetic acid, but 
has no influence on the tubular membrane, nor on the axis 
cylinder. 
2. Of the fine nerve-fibres which run in the same sheath 
with the dark-bordered fibres. 
I believe that no one, upon close observation, will doubt the 
existence of very fine nerve-fibres running in the same 
sheath with the dark-bordered fibres distributed to the skin 
of the frog. These fibres were described first by Dr. Beale,"^ 
who affirms that they exist not only in relation with almost 
all the dark-bordered fibres distributed to the tissues of the 
frog, but he also believes that they exist in vertrebata animals 
generally. As for myself, I can truly say that I, have seen 
such fine fibres running with peripheral dark-bordered fibres, 
both in several tissues of the frog and in the human skin. 
The fibres already mentioned become granular by the pro- 
longed action of acetic acid, and in refractive power they differ 
from the dark-bordered fibres. They vary in size, and they 
may be demonstrated more easily in the finer than in the 
larger bundles, because, in the finer, the dark-bordered fibres 
are far less numerous, and therefore the fine fibres are not 
hidden from sight. Each bundle of dark-bordered fibres con- 
tain several of them, but not all the bundles have the same 
number. They sometimes run among the dark-bordered 
fibres, and perhaps, on their way, cross them in different 
directions, but more frequently they are seen running between 
* 'Phil. Trans./ 1862, p. 900 ; see also 'Archives of Medicine,' No. xii, 
p. 247, and No. xiii, p. 13. 
