BLOOD. 221 



kidneys and liver, which we have assnmed to be consequent on 

 the raetamorpliosis of the blood-corpuscles ; for since the animal 

 matters undergo a chemical change by the elimination of the 

 carbon, the products which are then formed must be removed, 

 in order that the blood may retain its normal composition. 



In opposition to the assertion that the urea, uric acid, and 

 bilin are products of the metamorphosis of the blood-corpuscles, 

 it may be urged that the daily amount of these secretions in- 

 volves a larger daily consumption of blood-corpuscles than ap- 

 pears to be consistent with the rate of their reproduction, as far 

 at least as our knowledge of the act of formation of the corpus- 

 cles would lead us to infer. 



I liaA'e mentioned, in page 155, that the blood-corpuscles are 

 to be regarded as cells, Avhose development must be considered 

 as perfectly analogous with the development of other cells. In 

 absorbing from the plasma the substances requisite for their 

 nutrition, and in rejecting the products that must be conse- 

 quent upon the act of absorption, they ob\dously exert a modi- 

 fying influence on that fluid. The blood-corpuscles do not, 

 however, find their way into the circulating fluid in a matured 

 form, but their c}i;oblasts enter it as germs of the future cor- 

 puscles, and require the assistance of the atmospheric oxygen 

 to attain their perfect development. The only hypothesis we 

 can frame regarding the primary formation of the blood-cor- 

 puscles is, that they are produced from the plasma, that their 

 entire development and increase of bulk is due to the reciprocal 

 action of the young blood-corpuscular cells and plasma on 

 each other at the expense of the latter, and that up to the mo- 

 ment when the blood-corpuscles cease to discharge their func- 

 tions as independent organisms in the circulation, eveiy change 

 that occurs in them must be accompanied by a simultaneous 

 alteration in their cytoblastema, the plasma. 



It may further be urged that, in order to account for the forma- 

 tion and secretion of urea, uric acid, and bilin, there is no neces- 

 sity for the assumption that there is a metamorphosis of the blood- 

 corpuscles. These substances might as easily have been formed 

 in the process of chylification, or during the conversion of the chyle 

 into blood, or from the albumen, instead of from the corpuscles. 

 I have already mentioned that it is by no means probable 

 that these products of secretion are formed in the act of nutri- 



