ON THE EARLY STAGES OF INFLAMMATION 253 
the drawing. Yet many hours after the mustard had been removed, the pig- 
ment on which it had acted retained its stellate disposition, and the reticular 
appearance in the surrounding ring also remained unchanged, showing that the 
power of concentration had been permanently lost in those parts, and affording 
a favourable opportunity for obtaining by means of the camera lucida a delinea- 
tion of the medium, and both extreme conditions of the pigment in the same 
web. Next day the experiment was rendered still more instructive by the 
skin becoming excessively dark, the pigment undergoing full diffusion in the 
healthy parts of the web, so that the contrast between the ring about the con- 
gested area and the surrounding regions no longer existed: yet the stellate 
condition was still maintained where the mustard had lain, showing that it had 
suspended the faculty of diffusion no less than that of concentration. 
Croton oil now no longer seemed anomalous in its operation. Its curiously 
slow action upon the frog is comparable to the mild influence of the vapour 
of mustard, and the slight amount of inflammatory appearance which I had 
sometimes observed in a part where it had caused a great degree of pigmentary 
diffusion, is strictly analogous to the healthy state of the circulation in the 
reticular ring round the congested area in the last experiment. 
Cantharides also presents a parallel case. Its action is even more slow 
than that of croton oil; and on referring to notes taken at an early period 
in this investigation, I find that in one instance, when two hours and a half 
had elapsed after the application of a small drop of the tincture to the web, 
though diffusion of the pigment had become apparent in the area on which it 
had acted, no change of the blood had yet been observed ; and an hour and 
a half later, the red corpuscles, though abnormally adhesive as compared with 
those in surrounding parts of the web, were still moving slowly through the 
vessels. 
Hence it appears that diffusion of the pigment may be produced by either 
of these three substances without the blood undergoing any material derange- 
ment, and therefore that its occurrence under their influence is to a great extent, 
if not entirely, independent of the inflammatory process. On the other hand, 
it has been. demonstrated, as regards mustard, that when stagnation of the 
blood has been developed through its action, the state of the pigment-cells is 
the same as is induced by irritants generally, viz. a complete suspension of 
functional activity ; and, from analogy, we may be pretty sure that this is 
also true of croton oil and cantharides, although their slow operation renders 
it difficult to obtain absolute proof upon the point. 
In a physiological point of view, it is an interesting question, what is the 
cause of the diffusion of the pigment induced by these three irritants. I have 
