146 Circulation of the Blood 



persons see nothing less than the wonderful and almost 

 divine character of the natural operations as pro- 

 ceeding from the instrumentality of this common 

 agent, viz. the calidum innatum ; they farther regard 

 these spirits as of a sublime, lucid, ethereal, celestial, 

 or divine nature, and the bond of the soul ; even as the 

 vulgar and unlettered, when they do not comprehend 

 the causes of various effects, refer them to the imme- 

 diate interposition of the Deity. Whence they declare 

 that the heat perpetually flowing into the several parts 

 is in virtue of the influx of spirits through the channels 

 of the arteries ; as if the blood could neither move so 

 swiftly, nor penetrate so intimately, nor cherish so 

 effectually. And such faith do they put in this 

 opinion, such lengths are they carried by their belief, 

 that they deny the contents of the arteries to be blood ! 

 And then they proceed with trivial reasonings to 

 maintain that the arterial blood is of a peculiar kind, 

 or that the arteries are filled with such aereal spirits, 

 and not with blood ; all the while, in opposition to 

 everything which Galen has advanced against Erasi- 

 stratus, both on grounds of experiment and of reason. 

 But that arterial blood differs in nothing essential from 

 venous blood has been already sufficiently demonstrated; 

 and our senses likewise assure us that the blood and 

 spirits do not flow in the arteries separately and dis- 

 joined, but as one body. 



We have occasion to observe so often as our hands, 

 feet, or ears have become stiff and cold, that as they 

 recover again by the warmth that flows into them, they 

 acquire their natural colour and heat simultaneously ; 

 that the veins which had become small and shrunk, 

 swell visibly and enlarge, so that when they regain 

 their heat suddenly they become painful ; from which 

 it appears, that that which by its influx brings heat is 

 the same which causes repletion and colour ; now this 

 can be and is nothing but blood. 



When an artery and a vein are divided, any one may 



