262 I- \TI10LOGY OF 



By a simple hydraulic experiment it can be proved 

 that when the discharge from a tube is diminish^! 

 by a comparatively slight obstruction, the lateral or 

 distending pressure of the liquid situated behind the 

 seat of obstruction rapidly approximates to and 

 nearly equals the whole propelling force acting upon 

 that liquid.* And when studying the phenomena of 

 disordered circulation in the kidney, I obtained 

 abundant evidence of the operation of this physical 

 law in the hydraulic apparatus of the living body. 

 For on artificially disturbing the natural proportion 

 between the rate of supply of blood through the 

 renal artery and its rate of discharge through the 

 renal vein, the lateral or distending pressure of the 

 intervening liquid was so great, that the organ con- 

 tained an additional quantity of blood, equal, in some 

 instances, to twice its original weight. The en- 

 largement of the kidney in these experiments was, 

 of course, very great.* 



In congestion of the liver we also observe a rapid 

 and considerable enlargement as the result of ob- 

 struction to the free flow of blood through the hepatic 

 vessels. But when we proceed to study the operation 

 of the same physical principle in the blood-vessels of 

 the brain, we find its effects modified in a remarkable 

 manner by the peculiar position of that organ. For 

 however much the rate of efflux of blood through the 



O 



jugular veins may be diminished, however much the 

 rate of influx through the arteries may tend to 

 increase, the brain cannot inatcr'mUy enlarge; it cannot 

 burst the firm, unyielding walls which have grown 



* Vide iintr, pi'. 7:") ami i 



