272 ON THE EARLY STAGES OF INFLAMMATION 
and the causes which lead to it, being both, to a considerable extent, understood, 
the disease may, I think, be regarded as in so far satisfactorily explained. But 
one important lesson taught by the results of this investigation is, that it is 
necessary to draw a broad line of demarcation between inflammation produced 
by direct irritation, and that which is developed indirectly through the medium 
of the nervous system, whether in the immediate vicinity of a source of irrita- 
tion, as around a tight stitch in the skin, or a thorn in the finger, or at a distance 
from the disturbing cause, as when the kidneys are affected in consequence 
of the passing of a bougie, or the lungs through exposure of the feet to cold. 
Nothing can better illustrate the importance of this distinction, than what takes 
place in a recent wound. In consequence of the injury inflicted by the knife, 
together with the subsequent manipulation and exposure, the tissues, in a thin 
layer at the cut surface, are thrown into that condition which leads to effusion 
of liquor sanguinis, the fibrine of which, speedily coagulating, remains to con- 
stitute the bond of primary union, while the serum trickling away between the 
lips of the wound produces the discharge which soaks the dressing during the 
first twenty-four hours. But neither during the exudation of the lymph in 
such a case, nor during its subsequent organization, is there necessarily any 
inflammation induced in the lips of the wound through the nervous system ; 
and if this complication does occur, it interferes with the healing process in 
a degree proportioned to its intensity. In other words, while a certain amount 
of inflammation as caused by direct irritation is essential to primary union, any 
degree of it as induced indirectly is both unnecessary and injurious. 
The question how inflammation is developed through the medium of the 
nervous system, possesses a high degree of interest, in consequence of its bearing 
upon the manner in which counter-irritation operates therapeutically. In the 
integument, where we have the opportunity of seeing the affected part, the first 
indication of the supervention of inflammatory disorder around a centre of 
irritation is a blush of redness, which, as before shown,! consists, in the first 
instance, of mere dilatation of the arteries with rapid flow of blood through the 
capillaries. It is quite conceivable that arterial dilatation, carried to an extreme 
degree along with powerful action of the heart,? may so increase the tension 
upon the tissues as to impair their powers gradually by mechanical irritation, 
just as the frontal integument is affected by long-continued gentle pressure 
from without, as above alluded to; for we know that when inflammation does 
exist, mere increase of tension upon the blood in the vessels will greatly aggravate 
St DCe. Pp, ber 
* It is to be observed, that in the frog, when full dilatation of the arteries lasts for days together 
without the production of inflammatory congestion, the state of the vessels has been brought about 
by a very serious operation which greatly weakens the action of the heart. 
