ON THE EARLY STAGES OF INFLAMMATION 257 
the acid upon the tissues, I made the following experiment. Having killed 
a dark frog and amputated both legs, and ascertained by microscopic examina- 
tion that the pigment was fully diffused in the webs, I put one limb into a bottle 
of ‘ aerated water’ and the other into ordinary water: the latter soon became 
pale through post mortem concentration, but the former remained as dark as 
ever during the two hours for which it was retained in the solution of carbonic 
acid, the direct action of which upon the bloodless tissues was thus demonstrated. 
An hour after the limb had been taken out, however, it was evidently recovering, 
being distinctly lighter in colour than it had been, and two hours later it was 
quite pale, and the pigment in the webs was found to be in almost the extreme 
degree of concentration. In subsequent similar experiments I left the leg in 
the aerated water for a longer time, during which it always retained precisely 
the same tint that it had when first introduced ; and, if left for many hours, 
showed signs of loss of vitality, by the early supervention of cadaveric rigidity 
and exfoliation of the epidermis; but if it was taken out within about four 
hours, the pigment-cells recovered completely; and in one case a leg not 
removed for nine hours regained, nevertheless, to a considerable extent, the 
faculty of concentration. Thus it appears that carbonic acid, though exercising 
a powerful sedative influence upon the tissues, and paralysing for the time 
their vital energies, so as to give rise to intense inflammatory congestion, yet, 
even after a very protracted action, leaves them in a state susceptible of speedy 
recovery. 
Here we see for the first time a satisfactory solution of the much-debated 
problem of the cause of congestion of the lungs in asphyxia; for there can, 
I conceive, be no doubt that the pulmonary tissues, exposed under ordinary 
circumstances to the influence of a free supply of oxygen, suffer, like those of 
the frog’s web, from the vicinity of an abnormal proportion of carbonic acid, 
and inflammatory congestion is the necessary consequence. At the same time, 
the rapid recovery of the lungs from asphyxial congestion of considerable dura- 
tion, when the normal atmosphere is readmitted, finds an equally close parallel 
in the speedy return both of the pigment-cells and the blood to the healthy 
condition when the foot ot the frog is removed from the aerated water. 
But the most important lesson to be learnt from these simple experiments 
with carbonic acid upon amputated limbs, is that the tissues possess, indepen- 
dently of the central organs of the nervous system, or of the circulation, or even 
of the presence of blood within the vessels, an intrinsic power of recovery from 
irritation, when it has not been carried beyond a certain point; a principle of 
fundamental importance, which has never before, so far as I am aware, been 
+ This observation was made subsequently to the reading of the paper. 
LISTER ! ) 
