THE CIRCULATION OF THE BLOOD. 419 



declined in consequence of his age and infirmities. His doctrine soon 

 acquired popular currency ; it was, for instance, taken by Descartes 1 ' 

 as the basis of his physiology in his work On Man ; and Harvey had 

 the pleasure, which is* often denied to discoverers, of seeing his dis- 

 covery generally adopted during his lifetime. 



Sect. 4. Bearing of the Discovery on the Progress of Physiology. 



IN considering the intellectual processes by which Harvey's dis- 

 coveries were made, it is impossible not to notice, that the recognition 

 of a creative purpose, which, as we have said, appears in all sound 

 physiological reasonings, prevails eminently here. " I remember," 

 says Boyle, " that when I asked our famous Harvey what were the 

 things that induced him to think of a circulation of the blood, he an- 

 swered me, that when he took notice that the valves in the veins of 

 so many parts of the body were so placed, that they gave a free 

 passage to the blood towards the heart, but opposed the passage of 

 the venal blood the contrary way ; he was incited to imagine that so 

 provident a cause as Nature had not placed so many valves without 

 design ; and no design seemed more probable than that the blood 

 should be sent through the arteries, and return through the veins, 

 whose valves did not oppose its course that way." 



We may notice further, that this discovery implied the usual condi- 

 tions, distinct general notions, careful observation of many facts, and 

 the mental act of bring-ino- together these elements of truth. Harvey 



o o o * 



must have possessed clear views of the motions and pressures of a fluid 

 circulating in ramifying tubes, to enable him to see how the position 

 of valves, the pulsation of the heart, the effects of ligatures, of bleed- 

 ing, and of other circumstances, ought to manifest themselves in order 

 to confirm his view. That he referred to a multiplied and varied expe- 

 rience for the evidence that it was so confirmed, we have already said. 

 Like all the best philosophers of his time, he insists rigidly upon the 

 necessity of such experience. " In every science," he says, 18 " be it 

 what it will, a diligent observation is requisite, and sense itself must 

 be frequently consulted. We must not rely upon other men's expe- 

 rience, but our own, without which no man is a proper disciple of any 

 part of natural knowledge." And by publishing his experiments, he 

 trusts, he adds, that he has enabled his reader " to be an equitable 



JT Cuv. 53. 18 Generation of Animals, Pref. 



VOL. II. 29. 



