224 CIRCULATING FLUIDS : 



anide of potassium in the imnc of a horse two days after it 

 had been injected. Hence the whole mass of the blood occu- 

 pies a considerable time in passing through the renal arteries, 

 or else the kidneys do not remove all the foreign constituents 

 from the blood that passes through them. 



Others have calculated the rapidity of the circulation by the 

 quantity of blood projected by the heart at each systole. Reck- 

 oning this quantity at from 1 to 2 ounces, and the whole amount 

 of blood in the human body at 30 pounds, it would take from 

 3 to 7 minutes (assuming the pulse to be 75 in the minute) for 

 all this blood to pass through the heart. Since, however, the 

 blood in the smaller circles passes more frequently tlu'ough the 

 heart in a given time than the blood in the larger circles, and 

 since it is variously impeded and delayed in the different 

 organs, we must not consider that the absolute mass of the 

 blood of the Avhole body is represented by the identical 30 pounds 

 which pass through the heart in from 3 to 7 minutes. The 

 quantity of blood in an adult has likewise never been accurately 

 determined. Hales places it at 25 pounds ; the maximum is, 

 however, calculated to amount to 30 pounds ; and when we 

 consider the extremely large quantity of blood that is retained 

 in the capillary vessels, this estimate is probably too low. 



That the rapidity with which the blood circulates varies in- 

 versely with the distance from the heart is an established fact. 

 In the capillary system its progress is the most torpid. Omitting 

 the consideration of the various mechanical impediments that 

 meet the blood in the capillaries, it must be remembered that, 

 if the blood is the real nutrient fluid of the body, there must 

 be a necessary attraction between it and the organs it has to 

 nourish. The blood in the capillary network permeates the 

 tissues, or (to speak more correctly) the cells of the tissues at- 

 tract from the blood their proper nutriment. It is clear that 

 this must delay the course of the blood in the peripheral sys- 

 tem, to what amount it is impossible to say, but in all proba- 

 bility the delay will vary directly with the intensity of the ac- 

 tion between the blood and the tissues, and with the amount of 

 the change of matter. The greatest delay will most probably 

 occur in the kidneys and in the liver, since they afford the 

 largest amount of secreted matters. Even if the amoimt of the 

 secretions did not indicate a heightened cellular activity, it 



