EAftLY STAGES OF INFLAMMATION. 151 
sirable to confirm them by direct observation of the tissues. 
It fortunately happens that the pigmentary system of the 
frog is a tissue which, from its peculiar form and colour, is 
very apparent to the eye, so that it is easy to trace the re- 
markably active functions with which it is endowed, and their 
modifications under the influence of irritation.” 
The author then mentions the circumstances which led 
him to notice that the dark pigment of the frog presents re- 
markable differences of appearance at different times in one 
and the same animal ; each dark patch being sometimes of 
stellate figure with minutely ramifying rays, at other times in 
the form of a small rounded spot. These changes had been 
before observed by some German writers, who attributed the 
rounded form to contraction of the branching rays of a stel- 
late cell. This, however, the author finds to be erroneous, 
and in a supplementary section “on the anatomy and phy- 
siology of the pigmentary system of the frog,” shows that 
the cells never change in form or size, but that the pigment- 
granules which are suspended in a colourless fluid are capable 
of being, on the one hand, attracted by a central force into a 
small space in the body of the cell, and, on the other hand, 
dispersed by a repulsive power into the minutest recesses of 
the ramifying rays. Both concentration and diffusion of the 
pigment may take place with great rapidity, implying re- 
markable energy in the attractive and repulsive forces, both 
of which appear to reside in a nucleus. The supplementary 
section concludes with some remarks on the physiological 
importance of the actual observation of such attractions and 
repulsions in one of the animal tissues. 
The paper continues with an account of an experimental 
investigation into the effects of irritants upon this function 
of the pigmentary system. Many experiments are related, 
all tending to support the general proposition, that “ all 
agents, without any exception, which have the power of in- 
ducing accumulation of corpuscles and stagnation in the 
blood-vessels when applied to the web, paralyse at the same 
time the functions of the pigment-cells.” It is also shown, 
from experiments upon amputated limbs free from blood, 
that this effect is independent of the state of the circulation. 
In cases of slight irritation, in which the blood resumes, 
after a while, its natural characters (resolution takes place), 
the paralysis of the pigment-cells is only temporary. “ Thus 
the pigmentary system of the frog is a remarkably sensitive 
index of the condition of the affected tissue, and it is fortu- 
nate that its physical characters render it so easy to read its 
pointings. . . . The only other tissue of the frog’s web, 
