ON THE EARLY STAGES OF INFLAMMATION 267 
as in the English kind, the pale tint was not confined to the precise spot operated 
on, but affected a limited area of surrounding tissue ; whence it seems likely 
that it is developed through the medium of a local nervous apparatus contained 
in the skin.’ If this be true, we have no proof that the pigment-cells are capable 
of being stimulated except by nervous influence, although they are, as we have 
seen, peculiarly susceptible of suspension of function through the direct operation 
of irritants upon them. 
With regard to the nature of the change experienced by the tissues when 
temporarily deprived of power by irritants, the primary increase of motion 
of the cilia, lapsing into quiescence, under the operation of heat, may suggest 
the idea of exertion followed by exhaustion. But that the state of incapacity 
is not dependent on previous action, seems clear from the fact that in the pig- 
ment-cells it is maintained and aggravated by an irritant continuing in operation 
after complete suspension of function has been induced, the same kind of effect 
being still produced upon the tissues which are unable to act as upon healthy 
parts. As an illustration of this, I may revert to the results of immersion of an 
amputated limb in aerated water. The carbonic acid, as we have seen, entirely 
prevents the occurrence of post mortem concentration, implying that the powers 
of the chromatophorous cells are completely suspended by it within a few 
minutes at most of its first acting on the part ; yet, however long the tissues 
thus paralysed are kept subjected to its influence, they remain without any 
sign of action. They will, however, recover speedily and completely if soon 
taken out and exposed to the air, so that the irritating gas may be dissipated ; 
whereas if retained for several hours in the aerated water, they may, indeed, 
have their powers restored to a certain extent on removal from it, but exhibit 
only very feeble action. Such facts as these prove conclusively that the tissues 
may have their functional activity impaired without loss of vitality by the direct 
action of irritants, independently of any stimulating effects which may be at 
first produced by them ; and also that the influence thus exerted is of an in- 
jurious tendency. 
The imperceptible transition from suspension of function to loss of vitality 
displayed by the long-continued operation of carbonic acid upon the pigment- 
cells is also well illustrated by some of the experiments upon the cilia, especially 
those with heat and ammonia, which, unless employed with extreme caution, 
not only permanently arrested the vibratile filaments, but reduced the epithelium- 
cells to a condition in which they were amenable to the ordinary laws of chemical 
affinity. All irritants appear to be agents which, if operating with sufficient 
energy, completely destroy vitality, probably by inducing, through chemical 
* See the paper ‘On the Cutaneous Pigmentary System ’, before referred to, p. 48. 
