82 PHYSIOLOGY OF THE CIRCULATION. 



considering, that it is impossible to arrive at any 

 sati.-fartory conclusion as to the effects induced in 

 the former by the lateral pressure of the arterial 

 blood, without determining and bearing in mind 

 their distinctive peculiarities. They form a series 

 of minute porous tubes, the coats of which, being 

 highly contractile, are, in their healthy state, con- 

 tinually resisting the dilating pressure of the con- 

 tained blood. In their relation, therefore, to that 

 contained fluid, they represent so many rigid tubes. 

 In them there is consequently no considerable accu- 

 mulation of blood, nor do we find any functions per- 

 formed by the elasticity of their investing tissues. 

 But other and still more important effects are here 

 induced by the lateral pressure of the arterial blood ; 

 for by the operation of this force there is a constant 

 exudation of certain portions of the blood through 

 the thin and porous coats of these minute vessels. 

 For proofs, that compression of the blood in its 

 smaller vessels will cause its effusion through the 

 coats of the latter, and that the nature of this effusion 

 is mainly regulated by the degree of that compres- 

 sion, I beg to refer to a paper contained in the last 

 volume of the " Medico-Chirurgical Transactions:" 

 in it will be found an account of some experiments 

 in which, on directing an increased flow of blood 

 through one renal artery (by obstructing the abdo- 

 minal aorta and the blood-vessels of the other kidney), 

 various component parts of the blood, viz. liquid 

 albumen, fibrinous and coloured coagula, were found 

 in the secretion of the organ thus inordinately 

 supplied. 



