VOL. XXiri.] PHILOSOPHICAL TRANSACTIONS. 685 



the blood passing the extremities of the arteries and veins, I considered how to 

 preserve the blood in its vessels, that I might afterwards at any time see it in 

 their extremities when stagnant ; for this end, I caused several parts of the 

 mesentery to be tied on as many pieces of small round pill boxes, cut trans- 

 versely like little hoops ; on which, portions of the mesentery were extended 

 like tlie head of a drum; and on viewing them afterwards with the microscope 

 I found the extremities and branches of the blood-vessels charged with blood, 

 which before appeared in motion. On laying one of these parts of the mesen- 

 tery, thus expanded, in water, the stagnant blood in its vessels disappeared; but 

 on just immersing another of those pieces in water, I could with my naked eye 

 see the stagnant blood diffused in the interstices of the blood-vessels, and be- 

 tween the membranes of the mesentery: hence it is evident, that the blood may 

 pass the sides of its vessels after stagnation in them ; but whether its globules 

 are broken, or what figure renders them fit to pass those pores that are in the 

 sides of the vessels, I leave to the inquisitive. 



As the arteries are known to export the blood, so the veins return it back 

 again to the heart ; and here, as in the arteries, we find the common practice 

 of nature, in disposing the branches of veins to discharge the refluent blood 

 into the next adjacent trunk, and so on to the heart. And as the arteries afford 

 abundance of instances of checks given to the velocity of the current of the 

 blood through several parts, so the veins supply us with as many artifices to 

 assist its regular return to the heart, as well as favour those contrivances in the 

 arteries. 



The trunks of the carotid, vertebral, and splenic arteries are not only variously 

 contorted, but are also here and there dilated ; so the veins that correspond to 

 those arteries are also variously dilated. The beginnings of the internal jugulars 

 have a bulbous cavity, which are diverticula to the refluent blood in the sinuses 

 of the dura mater, lest it should descend too fast into the jugulars. The like 

 has been also noticed by Dr. Lower in the vertebral sinuses. The splenic vein 

 has divers cells opening into it near its extremities in human bodies ; but in 

 quadrupeds the cells open into the trunks of their splenic veins. 



The spermatic veins do more than equal the length of the arteries of the 

 testes in men; their various divisions, and several inosculations and their valves, 

 are admirably contrived to suspend the weight of the blood, in order to discharge 

 it into the larger trunks of the veins ; and were it not that the refluent blood 

 from the testes is a pondus to the influent blood from the arteries, and still 

 lessens its current in the testes ; these spermatic veins, like those of other 

 parts, might have discharged their blood into the next adjacent trunk. 



Who can avoid being surprised at the art of nature, in contriving the veins. 



