VOL. XXII.] PHILOSOPHICAL TRANSACTIONS. 467 



be be united with the artery de, as at c, and thus the blood be conveyed from 

 c to e ; be must be called a vein, and the blood coming to c, and being there 

 infused in ce, is the arterial blood, because it is carried there from the heart, it 

 being certain that dee is an artery. 



Amongst the rest Mr. L. had a tadpole before him, in which he could not 

 perceive any motion at all of the blood, how attentively soever he viewed it ; 

 of which at first no reason appeared ; till on contemplating this animal with 

 the naked eye, he observed that the fore-part of its body was contracted, by 

 which he imagined that the heart was oppressed so, that it could not force 

 out the blood, and receive it back again. While he was considering this, the 

 little animal made a very strong motion, beating its tail about, and bending his 

 body, by which it got clear of the oppression it was under; and on viewing it 

 again, he immediately perceived that the blood began to have a small motion 

 and impulse in several vessels, which increased so, as at length to come to its 

 motion, yet not with such velocity, as it would have had, if the body or the 

 heart had not been oppressed. The motion of the blood in these tadpoles ex- 

 ceeds all the rest of small animals and fish that Mr. L. has seen. 



Fig. 13, represents the tadpole of a frog, come to such a size, that it could 

 make use of both its legs ; and the fore legs were also discernible, but yet 

 covered with the skin. 



At last Mr. L. spied a small artery, which though it seemed so small, that 

 only one small red globule of blood could pass through it ; yet out of such a 

 branch of a vein there still proceeded two other branches, in each of which 

 the blood flowed, yet further asunder, and slower, than they had done before 

 they came into the separated vessels. After this, he fixed his eye on the great 

 artery and vein, which were so close to each other, that there was not above 

 the distance of the 4th part of the breadth of a hair between them ; and it 

 happening that the animal, when he was viewing it, moved its head upwards 

 and the tail downwards, the blood ran upwards in the artery, and downwards in 

 the vein, and that with an equal velocity ; yet, what was most remarkable was 

 to see the manifold small arteries, which proceeded from the great one, and 

 spread into several branches, and returning unite again in one, and which, at 

 last, poured out the blood again into the great vein. These particles of the 

 blood he computes, are so small, that a million of them cannot make up the 

 bulk of a large grain of sand ; and from thence may be conjectured, that such 

 small vessels have branches or channels ; for if they were not provided with 

 them, the blood vessels in the thinnest part of the tail, where they meet, would 

 not he cross one on another, but must unite, which has not been observed to 

 be the case. 



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