150 Circulation of the Blood 



medicines, give satisfactory reasons for the phenomena 

 that appear ; or who will not see that the precepts he 

 has received from his teachers are false ; or who thinks 

 it unseemly to give up accredited opinions ; or who 

 regards it as in some sort criminal to call in question 

 doctrines that have descended through a long succes- 

 sion of ages, and carry the authority of the ancients ; 

 to all of these I reply : that the facts cognizable by the 

 senses wait upon no opinions, and that the works of 

 nature bow to no antiquity for indeed there is nothing 

 either more ancient or of higher authority than nature. 

 To those who object to the circulation as throwing 

 obstacles in the way of their explanations of the 

 phenomena that occur in medical cases (and there 

 are persons who will not be content to take up with 

 a new system, unless it explains everything, as in 

 astronomy), and who oppose it with their own errone- 

 ous assumptions, such as that, if it be true, phlebotomy 

 cannot cause revulsion, seeing that the blood will still 

 continue to be forced into the affected part ; that the 

 passage of excrementitious matters and foul humours 

 through the heart, that most noble and principal viscus, 

 is to be apprehended ; that an efflux and excretion, 

 occasionally of foul and corrupt blood, takes place 

 from the same body, from different parts, even from 

 the same part and at the same time, which, were the 

 blood agitated by a continuous current, would be shaken 

 and effectually mixed in passing through the heart, and 

 many points of the like kind admitted in our medical 

 schools, which are seen to be repugnant to the doctrine 

 of the circulation, to them I shall not answer farther 

 here, than that the circulation is not always the same in 

 every place, and at every time, but is contingent upon 

 many circumstances : the more rapid or slower motion 

 of the blood, the strength or weakness of the heart as 

 the propelling organ, the quantity and quality or con- 

 stitution of the blood, the rigidity or laxity of the 

 tissues, and the like. A thicker blood, of course, 



