AND ANIMAL LIFE. 411 



while this resistance continues, the plethoric 

 state of the arteries must be constantly continued 

 and supported. As, however, the density of the 

 coats of the vessels, consisting chiefly of a cellu- 

 lar texture, is increased by pressure, so, in pro- 

 portion as the coats of the arteries are more ex- 

 posed to pressure by distention than those of the 

 veins, the former, in the progress of the growth 

 of the body, must increase much more in density 

 than the latter; and, therefore, the coats of the 

 arteries, in respect of density and resistance, 

 must come in time not only to be in balance 

 with those of the veins, but to prevail over 

 them."* 



CCCCXC1V. The preceding paragraph of Dr 

 CULL EN is beautifully ingenious ; but, if exa- 

 mined critically, will be found to be hypotheti- 

 cal or fallacious. The reasoning is intended to 

 show why hemoptysis does not happen after the 

 age of 35 years, and why the veins ultimately 

 become the seat of an affection similar to that 

 which has previously existed in the arteries. To 

 suppose, in the first place, that the coats of the 

 veins, in early life, have a greater proportional 

 density than those of the arteries, in order to ac- 

 count for the arterial flow of blood, is scarcely 

 consistent with the phenomena we observe in 

 the animal economy. 



* CULLEN'S First Lines, Vol. II. JDCCLX.VI. 



