462 PHILOSOPHICAL TRANSACTIONS. [aNNO I7O9. 



I have formerly communicated some discoveries relating to the circulation of 

 the blood in eels ; viz. that the blood, coming out of a great many small vessels 

 in the tail of an eel, is united in one greater blood-vessel, where the fish-bones 

 begin, and where the blood runs through a valve ; for I observed that the blood- 

 vein was not only moved in that part where the valve is, but also the parts 

 about it, of the breadth of 4 or 5 hairs breadth ; from whence it appeared, that 

 at every protrusion of blood into the heart through the valve, the blood stood 

 still for an instant of time, and then falling through the valve, it ran with great 

 swiftness, and was thickest just at its protrusion out of the valve, but ran 

 thinner or slenderer like the figure of a pear; and the vein that received this 

 protruded blood, was not entirely filled with it, but seemed for a small space to 

 be as it were empty, and its parts contracted ; and further observing it, I saw 

 the blood run slowly and leisurely along the same vessel. 



From this observation I imagined, that the same thing happens in the heart 

 of a human creature, viz. that there is a gentle and slow protrusion of the blood 

 out of the heart into that vessel, called the artery ; and consequently that there 

 is no such motion there, as is called a pulse, and which is felt in the extreme 

 parts of the body ; but that the pulses are only caused by the protrusion of the 

 blood through the valves in the veins; for I never observed any violent or swift 

 protrusion of the blood into the arteries, as often as I have viewed its cir- 

 culation : and though the blood, by the contraction of the heart, be suddenly 

 and hastily protruded out of it, yet it is slowly carried into the artery ; whereas, 

 on the contrary, it runs into the heart from the veins with a violent and swift 

 course : from whence it happens, I suppose, that the remaining part of the 

 blood in the veins, being unable to follow with so swift a motion, is, as it were, 

 violently and per saltum drawn or forced through the valves, and that it is this 

 sort of motion which we take for pulses in the arteries. 



To satisfy myself in the above observations, I have often viewed that sort of 

 motion in my arm, called the pulse, at the time when my body was without 

 motion and warm ; and I judged that the motion, which we perceived in the 

 blood vessel, was not derived from the heart to the hand, but contrariwise from 

 the hand to the arm, and so to the heart: from whence I concluded, that, like 

 as in the tail of an eel, there are no valves in the blood vessels, as far as I could 

 perceive, and that a great many small blood vessels, are, as it were, united in 

 that part where the fish bones begin, and make one large blood vessel, where 

 the first valve is ; in the same manner in human bodies, a great many single 

 blood vessels running out of the hand, are joined in the arm, where likewise 

 the first valve is, through which the blood at each protrusion falls into the 

 heart, producing what we call the pulse. 



