200 CIRCULATING FLUIDS: 



blood-corpuscles, it may be regarded as a substitute for the 

 portion of that constituent which has been taken up from the 

 blood for the nourishment of the tissues. 



From these observations we are led to conclude that there 

 is no necessary variation in the composition of venous and 

 arterial blood. The organism, when free from disturbing in- 

 fluences, possesses in itself various means of regulating the due 

 admixture of its different juices, and more especially of that 

 most important vital fluid, the blood. 



Amongst these means we may place the influence of the 

 nervous system, its power of increasing or lessening the action 

 of the secreting and excreting organs, and of inducing in them 

 either co-operating or vicarious action. 



The differences in the constitution of arterial and venous 

 blood cannot, however, by any possibility be very great. In 

 my analyses they usually fluctuate between fractions of a 

 hundredth part ; and they appear to be less between anah'ses 

 3 and 4, than between analyses 1 and 2, since the former 

 (anal. 3 and 4) were made on the blood of an old decrepid, 

 half-starved horse, in which the change and waste of tissue, 

 and the consequent metamorphosis of the blood, would be very 

 slight. That the difference must be small is obvious, when 

 we consider that the whole course of the circulation may be 

 accomplished in 25-30 seconds ; that the plasma just con- 

 veyed to the tissues must everywhere propel the nutrient mat- 

 ter conveyed there by the preceding blood-wave, and that the 

 tissues, everywhere saturated with nutrient plasma, only take 

 up a supply proportioned to their consumption. The process 

 of nutrition in the peripheral system is continuous and is sup- 

 ported by the liquid plasma with which all the tissues are sm-- 

 chargedj hence these tissues become the temporary recipients 

 of far more nutrient matter than they can possibly consume, 

 even as the rivulet contains infinitely more water than is ne- 

 cessary for the refreshment of the soil on its banks. 



In both cases we found that the venous blood contained a 

 larger proportion of solid constituents than the arterial ; hence 

 we infer that more Mater was removed by means of the 

 kidneys, liver, and skin, than had been supplied to the blood 

 by the nutrient fluids. 



The quantity of fil^rin in the venous blood in analysis 2 is 



