Itiquiry into the Nature and Properties of the Blood. 191 



" During this examination we took notice of a vessel ex- 

 tremely minute, issuing from the side of a larger, and turning 

 backwards from it in a curve line. We perceived at unequal 

 intervals sometimes one, sometimes two, and sometimes three 

 colourless globules, dropt or squeezed out of the larger ves- 

 sels into this minute one, and gliding through it singly and 

 very slowly; which made the Doctor imagine it might be a 

 secretmy duct. We observed likewise, that as the animal grew 

 languid, and near expiring, the blood in the arteries would 

 stop on a sudden, seem as it were coagulating, and then run 

 backwards for some time ; after which it would again recover 

 its natural course, with a great deal of rapidity." 



Mr.Leeuwenhoeck informs us that he saw, with great admi- 

 ration, in the furthest extremities of a very minute fish's tail, 

 how the larger arteries were there divided into the most fine 

 and evanescent ones ; and that many of the smallest veins re- 

 turning from the said extremities, met together at last in some 

 larger vein. There appeared also in some vessels such an 

 agitation of that blood (which was px'oti'uded from the larger 

 arteries towards the evanescent ones at the very extremity of 

 the tail, and returned afterwards through many minute veins into 

 a large one) as hardly can be conceived. In the larger arteries 

 he could perceive a continual new protrusion or accelera- 

 tion of the blood's course received from the heart ; but in the 

 smaller artex'ies the motion seemed equable without any such 

 repeated propulsion : and though in the minutest vessels there 

 appeared no colour, yet in the larger vein or artery, though 

 near the end of the tail, the blood was plainly red. The com- 

 munications of the arteries are sometimes direct with the veins, 

 without their terminations becoming previously evanescent, 

 and not to be traced. For the same curious observer tells us, 

 that on each side of the little gristles, which give a stiffness to 

 the tail of the fish, he could see a very open communication 

 of the veins and arteries ; the blood running towards the ex- 

 tremities through arteries, and returning back again through 

 veins that were evidently a continuation of those arteries, and 

 of the same diameter with them : and this he saw in thirty- 

 four different places, in as many arteries and as many veins. 

 The length of the whole fish was not half an inch ; yet in the 

 tail the circulation was notwithstanding visible in thirty-four 

 places, and the current of it in sixty-eight vessels ; and yet 

 these vessels were very far from being the most minute of all. 

 How inconceivable then must be the number of circulations 

 in the human body ! nor need we wonder to behold it issuing 

 forth at every puncture of a pin or needle. 

 [To be continued.] 



XXXVII. Reply 



