684 PHILOSOPHICAL TRANSACTIONS. [aNNO 1702. 



Nor can we reasonably doubt of the like patent communications of the arteries 

 and veins of human lungs and those of quadrupeds, when we consider that the 

 blood of their lungs must return to the heart in equal time and quantity, with 

 that of all the parts of the body besides. Hence it appears that the bronchial 

 blood vessels (first taken notice of by the accurate Ruysch) are absolutely 

 necessary, else the parts of the lungs could not receive nourishment ; nor could 

 the glands of the bronchia separate their liquor, if they were supplied with 

 blood from the pulmonic blood vessels, which is so quickly dispatched through 

 the lungs. 



On viewing the membrane that is between the toes of one of the hinder feet 

 of a live frog, after having frequently taken hold of the same leg of that animal, 

 to apply it to the microscope, I found that membrane very transparent, and 

 without any motion of the globules of the blood in it, as if the part had been 

 dead; but while I was looking on it, it was, I confess, not a little entertaining 

 to see the globules creep into it by degrees, and at length the blood move in all 

 the branches of its veins and arteries as before, when no violence had been 

 offered to the part ; while the blood is thus leisurely creeping through the 

 vessels, you may plainly see its globules compressed into oval figures, which are 

 made more or less oblong by the resistance those globules meet with, by the 

 contraction of the sides of the vessels they pass through; and this I have more 

 than once observed in the tails of the water newts or lizards ; but on examin- 

 ing the blood of these animals with a microscope, and comparing it with the 

 human blood, I found the globules of the lizard's blood more inclined to an oval 

 figure, and were as large again as the globules of human blood, and that of a 

 small fish, which I in like manner viewed at the same time. It is not unlikely 

 that a sudden retrocession of blood from the extremities of its vessels often 

 happens, and its circulation in the same vessels is afterwards carried on without 

 any impediment ; as on some passions of the mind, deliquiums by the effusion 

 of blood or otherwise. But if the blood is once become stagnant in its vessels, 

 especially the arteries, the part is in no small danger of a mortification ; unless 

 its neighbouring vessels, which enjoy the motion of the blood, drive on the 

 stagnant blood, and it escape by the sides of the vessels that retained it. Ex- 

 perience assures us, that in bruises when the blood is extravasated, it goes off 

 either by transcolation or else causes an abscess ; for there seems little reason 

 to suspect that any of the stagnant globules of the blood will be fit to re-unite 

 with the circulating mass. But that the blood after stagnation in its vessels 

 will sometimes pass their sides, appeared to me from the following experi- 

 ment. 



On viesving the mesentery of a dog when living, in which I had before seen 



