1 66 THE CIRCULATION. 



possible to say, at present, to what degree the discovery 

 may not influence all present notions regarding the nutri- 

 tion of the tissues, even in health. 



The circulation through the capillaries must, of necessity, 

 be largely influenced by that which occurs in the vessels on 

 either side of them. in the arteries or the veins ; their in- 

 termediate position causing them to feel at once, so to speak, 

 any alteration in the size or rate of the arterial or venous 

 blood-stream. Thus, the apparent contraction of the 

 capillaries, on the application of certain irritating sub- 

 stances, and during fear, and their dilatation in blushing, 

 may be referred to the action of the small arteries, rather 

 than to that of the capillaries themselves. But largely as 

 the capillaries are influenced by these, and by the con- 

 ditions of the parts which surround and support them, 

 their own endowments must not be disregarded. They 

 must be looked upon, not as mere passive canals for 

 the passage of blood, but as possessing endowments of 

 their own, in relation to the circulation. The capillary 

 wall is, according to Strieker, actively living and con- 

 tractile ; and there is no reason to doubt that, as such, it 

 must have an important influence in connection with that 

 nutritive exchange which goes on without cessation be- 

 tween the blood within and the tissues outside the capillary 

 vessel ; a process which, under the name of vital capillary 

 force, has long been recognised as one of the means con- 

 cerned in the circulation of the blood. 



The results of morbid action, as well as the phenomena of 

 health, strongly support the notion of the existence of 

 this so-called vital capillary attraction between the 

 blood and the tissues. For example, when the access 

 of oxygen to the lungs is prevented, the circulation 

 through the pulmonic capillaries is gradually retarded, the 

 blood-corpuscles cluster together, and their movement is 

 eventually almost arrested, even while the action of the 

 heart continues. In inflammation, also, the capillaries of 



