250 ON THE EARLY STAGES OF INFLAMMATION 
slight appearances of congestion. Chloroform also seemed at first still more 
anomalous in its operation, though in the opposite way; for though it was 
pre-eminently potent in inducing congestion, it caused no alteration whatever 
in the appearance of the pigment, whether mildly or strongly applied. 
Afterwards, as the true nature of the pigmentary functions became un- 
veiled, and further facts were developed, these difficulties were completely 
cleared away. The first step towards their solution was made in an experiment 
with ammonia. A frog being placed under chloroform, I covered the whole 
of the foot with sweet oil, except a small area in one of the webs, the pigment 
being in the stellate condition, i.e. about midway between perfect concentration 
and full diffusion. An assistant then held at a short distance above it a piece 
of lint soaked in the strongest liquor ammoniae, so that its pungent alkaline 
vapour might play upon the exposed area, while the rest of the foot was protected 
by the oil. This having been continued for a few seconds, accumulation of 
corpuscles and stagnation occurred in the vessels of the area, without any change 
in the appearance of the pigment. After a while, however, the creature happened 
to grow pale, and, in the web generally, the pigment became completely con- 
centrated so as to assume the dotted aspect, but in the part which was the seat 
of congestion it remained stellate as before. Hence it appeared that though 
the ammonia did not cause any change in the distribution of the pigment, it 
had in reality produced a great effect upon the chromatophorous cells, which, 
in the area exposed to its influence, had been deprived of the power of concen- 
tration by the mildest degree of action of the alkali that sufficed to induce 
stagnation of the blood. On examination of the web about four hours later, 
resolution of the stagnation was found to have taken place, though there was 
still some excess of corpuscles, with marked adhesiveness of the colourless ones 
in the vessels of the ammonia area. The creature was now released for the 
night. Next morning the integument was in the opposite extreme of colour, 
being almost black, and the pigment had the reticular appearance, being fully 
diffused throughout the whole web, except the central part of the ammonia area, 
where it retained the same stellate condition as the day before. Hence it ap- 
peared probable that the diffusive power, as well as the concentrating, had been 
paralysed by the ammonia, but had been recovered in all the area except the 
part that was likely to be the last to regain its functions. To ascertain whether 
the concentrating power had also been regained, I killed the frog and amputated 
the leg; soon after which the usual post mortem concentration took place 
completely in the web generally, while in the central part of the area the medium 
state was still retained, and in the rest of its extent concentration considerably 
beyond the medium state, but short of the full degree, supervened, showing 
