268 ON THE EARLY STAGES OF INFLAMMATION 
or physical action, an irreparable derangement of the molecular constitution 
of the tissues. Their essential property, however, is that of causing, when 
applied somewhat more mildly, a minor degree of disturbance or disorder in the 
component textures of the body, which are rendered for the time being unfit 
for discharging their wonted functions,! though afterwards, by virtue of their 
innate powers, capable of spontaneous recovery, the rapidity and completeness 
of which bears an inverse ratio to the intensity and duration of the previous 
irritation. Lastly, these same noxious agents, if in a still more gentle form, 
operate, upon some of the tissues at least, as stimulants, rousing them to in- 
creased exertion of their vital functions. How this effect is brought about must 
I believe, be only matter of uncertain speculation, so long as the real nature of 
life in the animal frame remains, as it probably ever will remain to our finite 
capacities, an impenetrable mystery. 
It is an interesting circumstance that, in the experiments with warm water, 
the cilia, after recovering from the state of quiescence, moved for a while more 
briskly than they did immediately before the application was made. This 
increased action cannot be attributed, like the primary acceleration resulting 
from very gentle warmth, to a mild operation of the irritant ; for the epithelium- 
cells must have been completely cooled down before it commenced. It must 
therefore be regarded as a true reaction on the part of the tissue, whether depen- 
dent on accumulation of vital energy during the period of suspended function, 
or excited, as by an irritant, by the state of disorder which the warm water 
had induced, seems uncertain. 
Considering the number and variety of the functions which direct observa- 
tion has shown to be suspended by irritants, viz. pigmentary concentration and 
diffusion, ciliary motion and nervous action, it appears probable that all the 
vital processes are liable to similar temporary arrest. 
Different tissues, however, seem to differ in the facility with which they 
are affected by irritants. The pigment-cells are very susceptible to their influence 
as is indicated by the complete paralysis which we have seen to be produced in 
them by agencies that give rise to only a minor degree of inflammatory con- 
gestion ; and also by the circumstance which I have often observed in the web 
of the frog, that, as in the choroid coat of the human eye, they become absorbed 
in parts which have been injured, having been deprived of vitality by causes 
which inflicted on other textures only a recoverable lesion. The epithelium- 
cells, too, are very sensitive to irritation, exhibiting its results more rapidly 
than can be accounted for merely by their exposed situation. In those which 
* The word ‘irritant’ is etymologically ill adapted to express the possession of this property ; 
but as it is universally employed in professional nomenclature, it is perhaps best to continue to use it. 
