76 ON THE MOTION OF THE BLOOD. 



gists have been convinced that the influence of the 

 heart could not reach the extreme arteries and the ori- 

 gins of the veins, they have ascribed the progression 

 of the blood in those vessels to a kind of oscillation, 

 and have happily employed this to demonstrate the 

 nature of inflammation. Many kinds of phenomena, 

 both physiological, as those regarding animal heat, 

 and pathological, as those observed in spasms and 

 particularly in fevers, favour the supposition of this 

 oscillatory faculty, though it is not demonstrable to 



the eye. (G) 



182. It remains now to enquire into the aid given to 

 the returning blood by the veins, not alluding at all to 

 their radicles. We should conclude at first sight that 

 they have less active power* than the rest of the san- 

 guiferous system, and that the return of their purple 

 blood to the heart is chiefly ascribable to the impetus 

 a tergo of the arterial blood, and to their valvular 

 structure which prevents any reflux. The efficacy 

 of the valves in this point of view, is shewn by the 

 distentions and infarctions of the veins in the lower 

 part of the abdomen, which are found destitute of 

 valves, f 



The existence of vital powers in the venous trunks 

 is probable, J from the example of the liver and pla- 



* What is commonly, but improperly, called the venous pulsation, observable 

 on opening living animals and in some morbid affections, and also under a 

 violent effort, does not correspond with the action of the heart, but with res- 

 piration; since if an expiration is unusually deep and lengthened, and the 

 reflux of the blood to the lungs thus impeded, the jugular vein swells as far as 

 the brain, the subclavian as far as the basilic, and the inferior cava as far as 



the crural. 



f- G. E. Stahl, De vena portte porta malorum. Halae. 1698. 4to. 

 J Lister, De humoribus. p. 25. 



