ROUX: FUNCTIONAL ADAPTATION 327 



vascular system, which has been thoroughly studied from 

 this point of view by Roux and Oppel (1910). 



It appears that only the very first rudiments of the 

 vascular system are laid down in the short first period of 

 automatic non-functional development. All the subsequent 

 growth and differentiation of the blood-vessels falls into the 

 second period, and is due wholly or in great part to direct 

 functional adaptation to the requirements of the tissues. 

 Thus from the rudiments formed in the first period there 

 sprout out the definitive vessels in direct adaptation to the 

 food-consumption of the tissues they are to supply. The 

 size, direction and intimate structure of these vessels are 

 accurately adjusted to the part they play in the economy 

 of the whole, and this adjustment is brought about 

 in virtue of the peculiar properties or reaction-capabilities 

 of the different tissues of which the blood-vessels are 

 composed. 



The properties which Roux finds himself compelled to 

 postulate in the vascular tissues, after a thorough-going 

 analysis of the different kinds of functional adaptation 

 shown by the blood-vessels, are summarised by him as 

 follows : 



"(i) The faculty depending on a direct sensibility 

 possessed by the endothelium and perhaps also by the other 

 layers of the intima of yielding to the impact of the blood, 

 so far as the external relations of the vessel permit. .In this 

 way the wall adapts itself to the hsemodynamically 

 conditioned 'natural' shape of the blood - stream, and 

 reaches this shape as nearly as possible." Through this 

 faculty of the lining tissue of the blood-vessels, the size of 

 the lumen and the direction of branching are so regulated as 

 to oppose the least possible resistance to the flow of the 

 blood. 



" (2) The faculty possessed by the endothelium of the 

 capillaries of each organ of adapting itself qualitatively to 

 the particular metabolism of the organ." This adaptedness 

 of the capillaries is, however, more usually an inherited state, 

 z>., brought about in the first period of development. 



"(3) The faculty possessed by the capillary walls of being 

 stimulated to sprout out and branch by increased functioning, 



Y 



