58 ON THE CUTANEOUS PIGMENTARY SYSTEM OF THE FROG 
the stellate condition in the webs, the tint of the skin being moderately dark ; 
and this state of things continued unchanged in both limbs for the next six 
hours. On the following day, however, the leg operated on was seen to be very 
dark, and the pigment in its webs was reticular ; while in the rest of the body the 
colour remained as before, and the pigment was still stellate. This striking 
contrast continued unaltered for two days, when it was destroyed by the body 
generally assuming the darkest possible tint. 
The diffusion of the pigment in consequence of division of nerves appeared 
to be the counterpart of the concentration by their irritation, and it seemed 
probable that the want of constancy in the results in the former case was 
caused, like the variable amount and duration of arterial dilatation after such 
operations,’ by the place of the divided trunks being supplied by other branches ; 
and that, if the nerves of a limb were all completely severed, diffusion would 
necessarily take place. With the view of testing the truth of this idea, the 
following experiment was performed. In the afternoon of October 10, 1857, 
I divided in a pale frog all the soft parts in the middle of the right thigh, except 
the femoral artery and vein and the sciatic nerve; and late in the evening, 
having ascertained that the circulation was going on freely in the webs, I cut 
the nerve also, no effect having been hitherto produced upon the colour of the 
limb. Next morning the body generally was still pale, but the right leg was 
black from the wound downwards. The same remarkable appearance con- 
tinued till the evening, when circulation ceased in the limb. On the 13th I per- 
formed the same experiment upon both thighs of another large pale frog, leaving 
the sciatic trunks entire in the first instance, until I had ascertained that the 
circulation in the feet had not been interfered with. Three hours after this 
had been done I divided the nerve in the left thigh, and in about forty minutes 
observed that the leg was decidedly darker below the seat of operation. After 
another hour I found the pigment stellate in the left webs, whereas it was in 
the dotted condition in the right foot. J then cut the nerve in the right limb, 
and within a quarter of an hour the leg was already considerably darker below 
the wound, and the pigment in the webs had become stellate. Next morning 
the body was still pale, but the legs were very dark, and they continued to 
deepen in tint, although the animal was kept in a white earthen jar covered 
with glass in a bright light, till at about 3 p.m. they were almost absolutely 
black, while the pigment was diffused in the webs to the extremest degree, 
the body meanwhile and the upper parts of the thighs retaining their former 
light colour. The tint of the legs remained unaltered till the death of the animal, 
which took place several hours later. 
Ts See) Di Sil. 
