226 CIRCULATING FLUIDS : 



puscle moves in the capillary system, and found that it tra- 

 versed a course of from 12 to 15 lines in the course of a minute. 

 If the motion of the corpuscles and of the iDlood is supposed to 

 be equal, and if the blood progresses in the large vascular trunks 

 at the rate of eight inches in one second, and consequently 480 

 inches in one minute, then the rapidity of the blood in the 

 larger trunks will be to the rapidity in the capillaries in the 

 ratio of from 480 — 384 : 1 ; a calculation tending to show that 

 the blood remains in the kidneys for a space of from one to 

 two hours. 



To this it may be objected that the phenomena of resorp- 

 tion are opposed to these results, and that if the renal veins 

 convey away as much blood as is conducted to the kidneys by 

 the renal arteries, this protracted delay would be impossible. 

 We cannot, however, determine with certainty the amount 

 of blood that enters the kidneys, for there is no necessity that 

 the whole mass of the blood should flow through them as through 

 the lungs ; moreover, only one branch of the aorta enters this 

 \'iscus, and while the tendency of the blood is to flow in the 

 direction in which it meets with the least opposition, there is, 

 perhaps, no organ in the whole body that ofii'ers a greater re- 

 sistance than the kidney. The chemical change that the blood 

 undergoes in the kidneys must likewise be much more rapid 

 than in the capillary vessels of many other tissues, since, in ad- 

 dition to the large amount of secretion that they yield, a por- 

 tion of the consumed blood is carried away by the lymphatic 

 vessels. 



Let us now endeavour to ascertain how long it would be ne- 

 cessary for the blood to remain in the kidney, in order that the 

 contents of the renal veins should exhibit chemical peculiarities 

 dependent on the action of the gland. Assuming that a healthy 

 man secretes about 40 ounces of urine in 24 hours, and that 

 the change dependent on the secretion of 10 oimces of urine 

 from 1000 ounces of blood may be detected by the changed 

 proportion of the water, then, omitting all consideration of the 

 lymphatic vessels, 4000 ounces of blood would pass through the 

 kidney in 24 hours, in order to separate 40 ounces of urine. 

 According to this calculation, 250 pounds of blood would pass 

 through the kidneys in 24 hours, about 10 pounds in one hour, 

 and 1 pound in six minutes ; and assuming that both kidneys 



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