CIRCULATION. 133 



and such actions are brought about, and such and such effects produced, 

 which can only be in the small arteries. When the blood is good and 

 genuine, the sensations of the arteries, or the dispositions for sensation, 

 are agreeable ; then the offices of the arteries are carried on suitably to 

 the intentions of nature. It is then that they dispose of the blood to 

 the best advantage, increasing the growth of the whole, supplying any 

 losses, keeping up a due succession [of organic particles], &c. 



The third use of the arteries, is that of secretion in all its various 

 forms. This must in some measure arise from stimuli which are of this 

 or that kind ; and from the arteries of particular parts being susceptible 

 of such and such stimuli. Without both uniting or concurring, secretion 

 could not take place. 



These actions depend upon a principle similar to that which is the 

 cause of the second use of arteries. 



The most perfect proofs of the actions of the arteries in propelling the 

 blood forwards, is in an aneurismal sac. If the artery above the sac be 

 compressed so as to prevent the blood flowing, the sac which was just 

 before pulsating and turgid shall immediately become flaccid and wholly 

 empty. Nothing could produce this but the action of the arteries 

 beyond the sac, and principally the smaller arteries 1 . 



Of the Continuation of Life in an Artery after the Animal is said to 



be killed. 



I injected the uterus of a cow that had been separated from the 

 body of the cow above twenty-four hours ; and I found next day that 

 it had contracted very much, and that the vessels had also contracted ; 

 for the great trunks were more turgid than when injected, so that the 

 injection had been squeezed back again 2 . This also shows that the 

 small vessels have a greater or a longer power of contraction than the 

 larger have. 



Origins of Arteries. 



The force of the blood's motion in an artery is stronger the nearer 

 to the heart, therefore it is reasonable to think that the situation of 

 the heart in the body is such as [that it should be nearest the parts 

 which] require the briskest circulation. But the difference in the 

 circulation, if there was nothing to retard it, would be too great for 

 the difference in the parts, as there are similar parts near and at a 



1 [In the production of this phenomenon Hunter assigns no share to the emptying 

 of the veins by the diastole of the heart and expansion of the chest.] 



2 [May not this be the effect of elasticity in consequence of the parts having been 

 put into hot water while being injected? I have seen that happen. — Wji. Glut.] 



