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latations and contractions of the vessel, it is combed 

 to the lungs, where it runs through every part of them. 

 The ramifications of the trachce* which are dispersed 

 in the viscera, carry thither a fresh and elastic air, which, 

 by acting on the lungs, dilates, winds them about, ex- 

 tends and opens them, and by that means facilitates the 

 course of the blood into the smallest ramifications of the 

 artery. Besides, being impregnated with this air, the 

 blood becomes thereby attenuated, is cooled, and re- 

 ceives a more lively co-lour. After its arrival at the ex- 

 tremities of the artery, it passes into that of the pulmo- 

 nary vein, which conducts it to the left ventricle of the 

 he-art. This latter, by contracting itself, pushes it into 

 the aorta, f which by continually dividing and subdivid- 

 ing itself, distributes this balsamic liquor to all the purts, 

 in order to promote their growth, or support, and oc* 

 casioti different secretions. 



2 1 . Such is the admirable mechanism of the circula- 

 tion of the blood in men, and in those animals which \ve 

 are best acquainted with. But how greatly does this 

 imperfect sketch fall short of the reality ! How incapa- 

 ble are these outlines of expressing the beauties of this 

 noble subject ! And who can account for the manner by 

 which the strength of life is repaired and recruited 1 

 Who can conceive the cause of that perpetual motion of 

 the heart, which continues without intermission for the 

 space of seventy, eighty, or a hundred years, which has 

 lasted for ages in the first race of men, and which re- 

 mains almost as long iti some species of animals 1 Havs 

 we discovered the exact part where the artery is changed 

 into a vein? Have we disclosed the mystery of the se- 

 cretion of those spirits, whose prodigious subtilty and 

 activity give them a near resemblance to light ? Can we 

 even determine in what manner the grosser secretions 

 arc performed ? Do we understand the true mechanism 



* The bronchia, t The principal trunk, of arteries. 

 fc'fi 



