IgO Of^ THE FUNCTION'S OF THE HEART AND ARTEEIES. 



the application of spirit of wine to a part of the membrane 

 of a frog's foot contracted the capillary arteries, and at the 

 same time accelerated the motion of the blood in them, 

 while in other parts, where inflammation was present, and 

 the vessels were distended, the motion of the blood was 

 slower than usual. 

 Another spe. Another species of inflammation may probably be occa- 

 wiaiion/" ^'"' sioned by a partial constriction or obstruction of the capil- 

 lary 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 extended to almost all the branches, belonging to some 

 small trunk, in which the pressure remains nearly equal to 

 the tension of the large arteries; for in this case it will hap- 

 pen, that the whole pressure will be continued throughout 

 the obstructed branches, without the subtraction of the 

 most considerable part, which is usually expended in over- 

 coming 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 circulation ; whence it may easily 

 happen, that they may be morbidly distended ; and this 

 distension may constitute an inflammation, attended by red- 

 ness and pain. Nor is it impossible, that obstructions of 

 this kind may originate in a vitiated state of the blood it- 

 self, 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 of- 

 ten 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 distensiori 

 / or increase of pressure : and this exception is sufficient to 

 explain another experiment 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 attended by less heat than the 

 former ; and where the obstruction is very great, it ma^ 



perhaps 



