4Q4 PHILOSOPHICAL TRANSACTIONS. [aNNO I7O9. 



^. of the greatest, he from thence shows how asthmatic people are very sensible 

 of this difference, especially when they breathe thicker ; for if they perform 

 their expiration in half the usual time, it will make this difference equal to 

 40lb. weight, which is almost equal to half the pressure of the air in ordinary 

 breathing. 



He next shows, how, from the great velocity of the blood, the friction on 

 the coats of the vessels, the impetus of the particles on one another, and 

 their elasticity, there must needs arise near the heart a strong intestine motion 

 in the blood, on which its heat depends ; and by consequence near the heart, 

 where the motion is greatest, the union of the particles will be in a great 

 measure hindered ; and therefore the particles that unite first, are such as have 

 the strongest attractive force, and such as have the least, are the last in uniting. 

 The particles endowed with the strongest attractive powers, are the most solid 

 and spherical corpuscles ; and their quantity of contact being the least, the se- 

 cretion they compose must be the most fluid: such is the liquor in the 

 pericardium. 



On the same principle, he gives the reason of the situation of the kidneys so 

 near the heart, that the salts in urine, being strongly attractive, and uniting 

 closely with the watery fluid, may quickly be drawn off from the blood. The 

 corpuscles which are slowest in uniting, must be such as have the weakest at- 

 tractive force ; which are such as have the least solidity, but their surfaces most 

 extended ; and therefore corpuscles, which have plain surfaces, are longer in 

 uniting than the spherical ones; but when united, they cohere most strongly, 

 and compose the most viscid fluids : such are the mucilages of the joints, which 

 are separated at the greatest distance from the heart. 



Though the secretion of the gall by the liver, and of the seed by the testi- 

 cles, may seem to be considerable objections against this doctrine, yet there is 

 really nothing that more illustrates and confirms it than the manner of forming 

 these secretions. Had the blood been immediately conveyed by the caeliac 

 artery to the liver, it is evident, on account of the nearness to the heart, 

 and the intestine motion of the blood, that so viscid a secretion, as the gall is, 

 could never have had time to be formed in the blood, and secerned in that 

 place ; and therefore here nature is forced to change her constant course of 

 sending blood to all parts by the arteries, and forms a vein, by which the 

 blood is derived to the liver from the branches of the mesenteric and caeliac 

 arteries, after it has passed through all the intestines, stomach, spleen, caul, 

 and pancreas. By this extraordinary contrivance, the blood is brought a great 

 way about before it arrives at the liver ; and its velocity being exceedingly di- 

 minished, the corpuscles have time to unite and form the gall. And here our 



