496 PHILOSOPHICAL TRANSACTIONS. [aNNO I7O9. 



were no other contrivance in it, the fluid which contains the largest particles, 

 will likewise consist of all the particles of the other secretions : but this incon- 

 venience is obviated, by imagining several tubes to arise from the side of the 

 canal or duct of the gland, whose orifices are of such dimensions, that they 

 will admit only particles which are smaller than those that are to be secerned by 

 the gland ; and a great many of them arising from the sides of the canal 

 throughout its whole circumvolution, will carry back to the blood the particles 

 which are of a less diameter than those have, which are to be secerned ; so 

 that there will at last remain in the gland only these particles, with such a 

 proportion of the watery fluid, as is necesssary for the proper fluidity of the 

 liquor to be secerned. 



In the discourse on the quantity of blood, he proves that the common opi- 

 nion, that there are only 15 or 20 lbs. of blood in the body, is founded on no 

 good grounds ; as it supposes, when an animal bleeds to death, that all the 

 blood in the body runs out of the wound, which the author shows to be false ; 

 for the larger the vessel that is wounded, the sooner must the animal die ; and 

 if the aorta itself were cut asunder, there would be a less effiision of blood 

 from it, than from a small artery : and from this he explains the true reason of 

 fainting on any sudden or violent evacuation, as in bleeding in the arm, cupping 

 in an ascites, &c. 



By blood he understands, not only the fluids in the veins and arteries, but 

 all the circulating liquors in the body, they being all parts of the blood, and 

 separated from it by the force of the heart, and many of them by the same 

 force returning again : and in order to estimate its quantity, he supposes that 

 the whole body is nothing but tubes or vessels full of blood, or of liquors de- 

 rived from it ; and then according to the various proportions of the thickness of 

 the coats of the vessels to their cavities, he calculates what the quantity of 

 blood must be; and finds, that if the body weigh l6o lbs. it must at least con- 

 tain 100 lb. weight of blood and such fluids. 



He next considers and determines the velocity of the blood. And first the 

 celerity by which it is thrown into the aorta, which he finds to be such as will 

 make it move 52 feet in a minute ; and because the sum of the section in 

 the branch of an artery, is always greater than that of the trunk, the velocity 

 of the blood must constantly decrease as the artery branches : And according 

 to the various proportions which the branches bear to the trunk, he calculates 

 the velocity at the extremities or evanescent arteries ; and finds, that if the 

 trunk always bore the proportion to the branches of 4 1,6 J 6 to 43,500, the 

 blood would move at least 4 times slower in the extremities, than in the great 

 artery : but if the proportion of the trunk to the branches, were always as 



