84 PHYSIOLOGY OF THE CIRCULATION. 



present the medium in which the latter are placed ; 

 and its resistance is evidently insufficient wholly to 

 repress, though it probably limits within certain 

 bounds, the tendency to effusion resulting from the 

 compression of the blood in the smaller arteries. 

 There is, therefore, from this source, a constant 

 effusion of albuminous fluid into the iutervascular 

 spaces, and a supply of their proper nutriment is 

 thus brought in immediate contact with the tissues 

 of the body. 



The absolute force of the lateral pressure of the 

 blood contained in the smaller arteries of a particular 

 part, will, equally with that of its onward pressure, 

 be affected by any change in the area of the main 

 arterial branch supplying them. Whatever, then, 

 increases the supply of blood to a part, will, at the 

 same time, increase the amount of lateral pressure 

 acting on the inner surface of the coats of the small 

 arteries of that part. The functions to which that 

 lateral pressure is there subservient, must conse- 

 quently, at this time also, be performed with unusual 

 activity. And this reasoning is fully corroborated 

 by the connexion invariably observed in health and 

 in disease between the activity of the nutritive 

 process and the rate of supply of blood to a part, as 

 estimated by the number and calibre of the arterial 

 trunks connected with it. 



A similar preponderance of the pressure acting 

 on the internal siirface of the coats of the smaller 

 arteries will undoubtedly assist in causing that sepa- 

 ration or exudation of certain portions of the blood 

 which constitutes the first stage in the processes of 



