=. SSS 
ON THE EARLY STAGES OF INFLAMMATION 259 
intense inflammation in the human subject is, however, familiar to all. All of 
them also afforded, in their effects upon the pigment-cells, ocular evidence of 
impairment of the functional activity of the tissues on which they act; and 
considering the number included in the list, and their great variety in essential 
nature, we need not hesitate to admit that similar effects are produced by the 
entire class of irritants. 
There is another tissue in the frog’s web which discharges functions apparent 
to the eye, viz. the arterial muscular fibre-cells, the contractions of which are 
readily recognized in consequence of the changes of calibre which they produce 
in the vessels ; and the manner in which the arteries are affected in a congested 
part of the web indicates that the muscular, like the pigmentary tissue, has 
its functional activity impaired by a certain amount of irritation. Thus I have 
repeatedly been struck with the fact, and noted it before I knew its significance, 
that an artery running through a limited area on which an irritant has acted, 
remains dilated in the spot, although it may vary in other parts of its course. 
This I have observed in one experiment with mustard, in one with acetic acid, 
in two with ammonia, and in one with heat. In the last-mentioned case the 
appearance was particularly striking, from the circumstance that two arteries 
happened to pass through the burnt part, and were constricted to absolute 
closure in the rest of their course, contrasting strongly with their fully dilated 
state within the area. 
In the ammonia experiments also the artery concerned was, in the progress 
of each case, seen to be completely constricted beyond the congested area, 
though still dilated within it. The limitation of this effect on the arteries, to 
the extent of the part acted on by the irritant, proves that it is the result of 
its direct action on the tissues ; differing remarkably in this respect from the 
dilatation of the vessels, which is produced indirectly through the medium of 
the nervous system, and affects a wide space round about the spot irritated. 
But with regard to both the muscular fibre-cells of the arteries and the 
pigment-cells, it may fairly be questioned whether the diminution of power to 
act resides in them or in those portions of their nerves which are situated in the 
irritated region. The view that the nerves are paralysed by irritants is con- 
sistent with the benumbing influence well known to be exerted upon the human 
skin or mucous membranes by some of those agents, e.g. mechanical violence, 
the galvanic shock, cold, and chloroform. I have also observed, as before 
* The only experiment which I made with cold was performed by introducing a test-tube, contain- 
ing a dark amputated limb, into a freezing mixture of ice and salt at about 20° Fahr. for ten minutes. 
When the frozen limb had thawed, I ascertained, on microscopic examination, that the pigment had 
undergone a slight degree of post mortem concentration, but five hours later it was still in much the 
same condition. 
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