16 
CiAcciOj on the Distribution of 
is^ the nuclei connected with capiilary walls can hardly be dis- 
cerned ; for we can find no means to colour them deeper so 
that they may be rendered visible after the addition of a little 
diluted acetic acid. It is evident^ therefore^ that the capilla- 
ries must be injected with Prussian blue, if we wish to ascertain 
the number and size of the nuclei connected with their walls_, 
because^ by soaking afterwards the blue injected capillaries 
in an ammoniacal carmine solution^ their nuclei^ by being co- 
loured red^ are clearly displayed. 
Having given this outline of the process I have followed 
in carrying out the present inquiry, I proceed now to detail 
the results of my observations on the distribution of nerves 
to the skin of the frog, and I think it will be convenient to 
arrange the subject under the following heads : — 
1. Of the dark-bordered nerve-fibres, their course, and the 
manner in which they terminate. 
2. Of the fine nerve-fibres, which run in the same sheath 
with the dark-bordered fibres. 
3. Of the nerve fibres distributed to the capillary vessels. 
4. Of the nature and origin of the fine nerve-fibres travel- 
ling in company with the dark-bordered fibres. 
1. Of the dark-bordered nerve-fibres, their course, and the 
manner in which they terminate. 
When the inner layer of the derma of a frog is examined 
with a power magnifying from 200 to 350 diameters, a con- 
siderable number of dark-bordered nerve-fibres may be ob- 
served, which are arranged in bundles of difi'erent sizes. Each 
bundle consists of a hyaline investment of connective tissue, 
and of two or more dark bordered fibres. I have seen, but 
rarely, small bundles containing a single large dark-bordered 
fibre. The primitive nerve-fibres of which the bundles are 
composed, vary much in size, and sometimes exhibit a slight 
waviness of their margins, and sometimes, at irregular inter- 
vals, varicosities. These varicosities vary greatly both in size 
and shape, and very probably are not natural, but depend on 
the change which takes place soon after death in nerve-fibres 
generally, or on the method adopted in the preparation of the 
specimens. The primitive fibres of each bundle not unfre- 
quently lie parallel to each other, but sometimes fibres are 
seen to pass from the one side of the sheath to another, cross- 
ing other fibres more or less obliquely. Some fibres, while 
running in the sheath, are seen actually to divide, and the di- 
vision often occurs at the point whereat the bundle bifurcates. 
