132 CIRCULATION OF THE BLOOD. 



conception of the subject from the evidence of his own eyes, is vir- 

 tually blind to all that concerns anatomy, and unfit to appreciate 

 what is founded thereon ; he knows nothing of that which 

 occupies the attention of the anatomist, nor of the principles 

 inherent in the nature of the things which guide him in his 

 reasonings; facts and inferences as well as their sources are 

 alike unknown to such a one. But no kind of science can pos- 

 sibly flow, save from some pre-existing knowledge of more ob- 

 vious things ; and this is one main reason why our science in 

 regard to the nature of celestial bodies, is so uncertain and con- 

 jectural. I would ask of those who profess a knowledge of 

 the causes of all things, why the two eyes keep constantly 

 moving together, up or down, to this side or to that, and not 

 independently, one looking this way another that; why the two 

 auricles of the heart contract simultaneously, and the like? 

 Are fevers, pestilence, and the wonderful properties of various 

 medicines to be denied because their causes are unknown? Who 

 can tell us why the foetus in utero, breathing no air up to the 

 tenth month of its existence, is yet not suffocated? born in 

 the course of the seventh or eighth month, and having once 

 breathed, it is nevertheless speedily suffocated if its respiration 

 be interrupted. Why can the foetus still contained within the 

 uterus, or enveloped in the membranes, live without respira- 

 tion; whilst once exposed to the air, unless it breathes it in- 

 evitably dies? 1 



Observing that many hesitate to acknowledge the circulation, 

 and others oppose it, because, as I conceive, they have not 

 rightly understood me, I shall here recapitulate briefly what I 

 have said in my work on the Motion of the Heart and Blood. 

 The blood contained in the veins, in its magazine, and where 

 it is collected in largest quantity, viz., in the vena cava, close 

 to the base of the heart and right auricle, gradually increasing 

 in temperature by its internal heat, and becoming attenuated, 

 swells and rises like bodies in a state of fermentation, whereby 

 the auricle being dilated, and then contracting, in virtue of its 

 pulsative power, forthwith delivers its charge into the right 

 ventricle; which being filled, and the systole ensuing, the 

 charge, hindered from returning into the auricle by the 



1 Vide Chapter VI, of the Disq. on the Motion of the Heart and Blood. 



