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2. It is proved by the results of intercepting the supply of 

 arterial Wood to the structures that the life of these parts can- 

 not be supported without it. In some instances this is shewn by 

 direct experiment, as by ligatures upon the arterial trunks through 

 which blood is conveyed to the seat which might be the subject of 

 the observation. In other instances which have never been sub- 

 jected to this test, the necessity of arterial blood to the support of 

 life is inferred agreeably with the results just hinted at. 



3. Unless the tendons, &c. form exceptions, there is no struc- 

 ture which is not composed of tubuli, communicating with the 

 arteries. But the extremities or minute communications differ in 

 many respects from the trunks : hence, as the continuity of a vascular 

 system is extended, the tubes composing it are arranged into several 

 orders, exercise different functions, hold different relations, and ex- 

 hibit phenomena peculiar to each. That all structures are com- 

 posed of tubuli continuous with the arteries is inferred on these 

 grounds: 1st, that the life of the parts in question would not be 

 preserved if this continuity were interrupted ; 2nd, that all parts dis- 

 play the phenomena of growth, and require the processes of 

 nutrition; 3rd, that all parts are .permeated by fluids, all of which 

 results are dependent upon the supply of blood. If any parts 

 .ire nourished by porous absorption, the argument is not by such 

 fact invalidated, as it is of no consequence whether the fluids pass 

 into such parts through an uninterrupted tube, or whether by 

 proximity of the openings jute vessels,, or by the arrangement of an 

 intervening structure performing the office of an uninterrupted 

 tube, by an intermediate .channel. The communication of the com* 

 ponent tubuli of every structure with the arteries is preserved, and 

 this is all I now stipulate for. 



