CIRCULATION OF THE BLOOD. 123 



to be sought. Meantime I would only ask, how many things 

 we admit in physiology, pathology, and therapeutics, the causes 

 of which are unknown to us ? That there are many, no one 

 doubts the causes of putrid fevers, of revulsions, of the pur- 

 gation of excrementitious matters, among the number. 



Whoever, therefore, sets himself in opposition to the circula- 

 tion, because, if it be acknowledged, he cannot account for a 

 variety of medical problems, nor in the treatment of diseases 

 and the administration of 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 re- 

 gards it as in some sort criminal to call in question doctrines 

 that have descended through a long succession 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 erroneous assumptions, such as that, if it be true, phle- 

 botomy 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 circu- 

 lation 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- 



