MALPIGHI, SWAMMERDAM, LEEUWENHOEK. 581 



ceived 375 letters and papers." "The works themselves, except that 

 they lie in the domain jf natural history, are disconnected and appear 

 in no order of systematized study. The philosopher was led by what 

 transpired at any moment to lead him." 



In 1GS6 he observed the minute circulation and demonstrated the 

 capillary connection between arteries and veins. This was perhaps 

 his most important observation for its bearing on physiology. It must 

 be remembered that Harvey had not actually seen the circulation of 

 the blood, which he announced in 1628. He assumed on entirely suffi- 

 cient grounds the existence of a complete circulation, but there was 

 wanting in his scheme the direct ocular proof of the passage of blood 

 from arteries to veins. This was supplied by Leeuwenhoek. Fig. 8 

 si mws one of his sketches of the capillary circulation. In his efforts 

 to see the circulation he tried various animals; the comb of the young 

 cock, the ears of white rabbits, the membraneous wing of the hat were 

 progressively examined. The next advance came when he directed 

 his microscope to the tail of the tadpole. Upon examining this he 

 exclaims: 



"A sight presented itself more delightful than any mine eyes had 

 ever beheld; for here I discovered more than fifty circulations of the 

 blood, in different places, while the animal lav quiet in the water, and 

 I could bring it before my microscope to my wish. For I saw not only 

 that in many places the blood was conveyed through exceedingly mi- 

 nute vessels, from the middle of the tail towards the edges, but that each 

 of the vessels had a curve or turning, and carried the blood back 

 towards the middle of the tail, in order to be again conveyed to the 

 heart. Hereby it plainly appeared to me that the blood-vessels which 

 I now saw in the animal, and which bear the names of arteries and 

 veins, are, in fact, one and the same; that is to say, that they are 

 properly termed arteries so long as they convey the blood to the 

 furtherest extremities of its vessels, and veins when they bring it back 

 to the heart. And thus it appears that an artery and a vein are one 

 and the same vessel prolonged or extended." 



This description shows that he fully appreciated the course of the 

 minute vascular circulation and the nature of the communication be- 

 tween arteries and veins. He afterwards extended his observations to 

 the web of the frog's foot, the tail of young fishes and eels. 



In this connection it should be remembered that Malpighi, in 1661, 

 observed the flow of blood in the lungs and mesentery of the frog, but 

 he made little of it. Leeuwenhoek did much more with his discovery, 

 and gave the first clear idea of the capillary circulation. Leeuwenhoek 

 was also anticipated by Malpighi in reference to the microscopic struc- 

 ture of the blood. (See also under Swammerdam.) To Malpighi the 

 corpuscles appeared to be globules of fat, while Leeuwenhoek noted 

 that the blood discs of birds, frogs and fishes were oval in outline and 



