ON THEIPBPARLY STAGES OF INFLAMMATION 7g fs 
But a comprehensive and complete account of the inflammatory process 
must embrace not merely the state to which the tissues are brought when the 
disease is fairly established, but also the causes which lead to it. 
Inflammation is sometimes brought about in man in a way strictly analogous 
to that in which we induce it in the web of the frog’s foot, viz. by the immediate 
operation of some noxious agent from without, as when boiling water is poured 
upon the skin. One peculiarity connected with such cases, as compared with 
those which are of idiopathic origin, is the great rapidity with which the various 
stages of the disorder are often developed. This, however, is the natural con- 
sequence of the direct manner in which the prejudicial influence is exerted 
upon the tissues ; the inflammatory phenomena supervening more speedily in 
proportion to the energy of the irritant. This principle is well illustrated by 
the effects of mechanical violence upon the human integument. A moderate 
degree of pressure applied continuously gives rise, during the first few hours, 
to nothing more than inflammatory congestion, which disappears soon after the 
pressure has been removed, as seen in the red mark produced upon the forehead 
by a tightly fitting hat. But if such treatment be continued for a considerably 
longer period, vesication will result, as when apparatus employed for the treat- 
ment of fractures is applied too firmly for many hours together over a bony 
prominence. The same effect which is thus slowly developed under a moderate 
degree of mechanical irritation, may, however, be induced very rapidly through 
the same agency in a more intense form, as is shown by the bullae which are 
often observed in surgical practice very soon after the infliction of a severe 
contusion. Here the source of irritation being no longer in operation, there is 
no blush of redness in the vicinity dependent upon arterial dilatation, and hence 
such cases are often supposed to have nothing in common with inflammation ; 
and I have known these vesicles mistaken for evidence of gangrene, so as to 
lead to unnecessary amputation. The suddenness with which inflammatory 
oedema arises in consequence of the bites or stings of venomous reptiles is ex- 
plicable on the same principle. The poison appears to diffuse itself among 
the tissues so as to operate directly upon them, and when extremely virulent, 
kills them outright ; but when less potent, produces merely a temporary though 
rapid prostration of their vital energies with consequent inflammatory effusion. 
Again, the congestion of the lungs, which comes on so quickly in asphyxia, has 
been before alluded to’ as probably the result of the sedative influence which, 
from experiments upon the frog, we are led to believe must be produced upon 
the pulmonary tissue by the abnormal amount of carbonic acid in the air-cells. 
In the class of cases hitherto considered, the derangement of the part, 
1 ae 
Seep. 257. 
