ON THE CUPANEOUS  PIGMPNTARY SYSTEM OF THE FROG 57 
system,’ as is evident from the effects produced on the colour of the skin by 
a struggle on the part of the animal. 
Much attention has been devoted by von Wittich to the inquiry, by what 
ganglionic centres this control is exercised. He found that division of the 
sciatic nerve in the thigh, or of cutaneous branches in the dorsal region, did 
not prevent the parts of the skin supplied by them varying in colour along 
with the rest of the body under the influence of light ; and, supposing that in 
such operations all connexion was severed between the portions of integu- 
ment concerned and the central organs of the nervous system, he inferred 
that the pigmentary changes induced by light were effected independently 
of either the cerebro-spinal axis or the usually recognized sympathetic ganglia. 
He nevertheless regarded such variations as probably reflex in their nature, 
and attributed them to a peripheral ganglionic apparatus in the skin itself; 
and this opinion appeared confirmed by the circumstance that direct irritation 
operated in the same manner upon the colour of a detached piece of integument 
as upon that of the living animal. At the same time, as he observed paleness 
of tint to result from irritation of the cord, or of the nerves distributed to a parti- 
cular part of the surface, he concluded that the spinal system was also capable 
of acting on the pigment-cells, and so accounted for the supposed influence of 
psychical excitement upon the tint of the skin. Thus, according to his view, the 
cutaneous pigmentary system was circumstanced like the heart or intestines, 
which, though possessing the faculty of independent action by virtue of their 
intrinsic ganglia, may also have their movements affected by mental emotion. 
In the course of some experiments performed in April 1857, with reference 
to the influence exerted by the cord upon the calibre of the arteries, I noticed 
on two occasions that partial division of the roots of the nerves for one of the 
hind legs within the spinal canal was immediately followed by increased pale- 
ness of the limb, of transient character, after which the leg assumed precisely 
the same colour as the other, this result being in accordance with von Wittich’s 
description. But I further observed in two cases in which such operations 
had been performed, that when a considerable time had elaspsed, viz. nine hours 
in one instance and two days in the other, the limb whose nerves had been 
cut was decidedly darker than the rest of the body. Similar results were once 
obtained from the division of the sciatic nerve in the thigh. When the opera- 
tion was performed, viz. at 45 30™ p.m. on April 4, 1857, the pigment was in 
1 The part of the paper devoted to this branch of the subject has been entirely rewritten ; and 
the dates in the text imply that most of the observations with reference to it have been made since 
the reading of the manuscript before the Society. 
* Vide Miller’s Archiv, loc. cit., p. 56. 
