of the Heart and Arteries . 27 
sioned by a partial constriction or obstruction of the capillary 
arteries, which must indeed be supposed to exist where the 
blood has become wholly stagnant, as Dr. Wilson in some 
instances found it. This obstruction must however be ex- 
tended to almost all the branches, belonging to some small 
trunk, in which the pressure remains nearly equal to the ten- 
sion of the large arteries ; for in this case it will happen, that 
the whole pressure will be continued throughout the obstruct- 
ed branches, without the subtraction of the most considerable 
part, which is usually expended in overcoming the resistances 
dependent on the velocity ; so that the small branches will be 
subjected to a pressure, many times greater than that which 
they are intended to withstand in the natural state of the cir- 
culation ; whence it may easily happen that they may be mor- 
bidly distended ; and this distension may constitute an inflam- 
mation, attended by redness and pain. Nor is it impossible, 
that obstructions of this kind may originate in a vitiated state 
of the blood itself, although it would be difficult to prove the 
truth of the conjecture ; it seems, however, to be favoured by 
the observation of Haller, that little clots of globules may 
often be observed in the arteries, when the circulation is lan- 
guid, and that they disappear when its vigour is restored, 
especially after venesection. But if a very small number only 
of capillary arteries be obstructed, other minute branches will 
still be capable of receiving the blood, which ought to pass 
through them, without any great distension or increase of 
pressure : and this exception is sufficient to explain another ex- 
periment of Dr. Wilson, in which a small obstruction, caused 
by puncturing a membrane with a hot needle, failed to excite 
an inflammation. This species of inflammation is probably 
E 2 
