220 CIRCULATING FLUIDS : 



secretions of animals of nearly every form of structure, and 

 under sucli varying phases of existence. 



I will now proceed seriatim Avith the objections that may be 

 urged against my views respecting the metamorphosis of the 

 blood. 



Analyses of the urine show us that it contains a greater 

 amount of urea and uric acid than of extractive matters ; as- 

 suming that the former substances, and the bilin, are products 

 of the metamorphosis of the blood-corpuscles, and that the 

 latter are the products of the change that the plasma under- 

 goes in the nutrition of the peripheral system, the mass of the 

 former is greater than the mass of the latter. If, moreover, 

 a portion of the extractive matter is in reality not removed by 

 the kidneys, but is, as I have already suggested, in page 150, 

 again adapted in the circulation to the purposes of nutrition, 

 (serving probably for the cytoblastema of the cells of the cartila- 

 ginous and gelatinous tissues), then the separation of so consi- 

 derable a quantity of the product of the metamorphosis of the 

 blood-corpuscles ought still to surprise us, if its only purpose 

 were to supply the fibrin, and possibly a part of the consumed 

 albumen in the plasma. 



It can, however, be easily shown that another and a much more 

 important final result must be considered in the consumption of 

 the blood-corpuscles. For if, as I have shown, in page 155, 

 the blood-corpuscles are principally concerned in the consump- 

 tion of the atmospheric oxygen, then it is clear that the greater 

 part of the carbon, which is exhaled from the lungs as carbonic 

 acid, must originate from them, and the source of animal heat 

 would thus be chiefly attributable to the metamorphosis of the 

 blood-corpuscles. Consequently, the chemical modifications of 

 the blood-corpuscles are of at least as much importance as the 

 act of nutrition in the peripheral system carried on by the 

 agency of the plasma, inasmuch as they are subser^dent to the 

 most essential and indispensable requisite for animal life. The 

 other purposes of the corpuscles appear also to be subservient 

 to this great end. 



If the blood-corpuscles (from the period of their develop- 

 ment up to their final solution) convert as large a quantity of 

 carbon as is generally assumed, into carbonic acid, in order to 

 maintain a proper degree of temperature, then we cannot be 

 astonished at the amount of the products of secretion of the 



