172 THE FLUIDS. 



through the ramifications of the tracheae, which open upon the sur- 

 face of their bodies. 



Lehmann's idea, that the blood-cells are laboratories in which the 

 individual constituents of the plasma are prepared for the higher 

 function of aiding in the formation and reproduction of the tissues, 

 is scarcely tenable, since the nutrition of the tissues is equally per- 

 fect, so far as can be perceived, in animals whose blood is destitute 

 of this histological element. Indeed, that the red corpuscles have 

 any direct relation to the formation of the tissues, is very impro- 

 bable; cfes-assimilation and the consequent development of vital 

 force being, it is believed, their special function. 



We have no certain knowledge of the length of time the blood- 

 cells exist. Since the cells of the same blood differ in the length 

 of time during which they resist chemical agents, it is probable that 

 the more easily decomposed, and which are usually of a deeper 

 color, are the older ; while the paler and less easily acted upon, and 

 which present in their granules the rudiments of a nucleus, are of 

 more recent origin. That their regeneration is not very rapidly 

 effected is probable, from the fact that the blood is poor in corpuscles 

 for several days after a moderate venesection, and exhibits a great 

 deficiency of them for a prolonged period after repeated bleedings ; 

 and since there is a copious supply of colorless corpuscles after 

 severe losses of blood. If, however, they are slowly regenerated, 

 they cannot have a very short existence, since otherwise the num- 

 ber of the colored cells would not so far exceed that of the colorless 

 corpuscles. (Lehmann.) 



Whether the blood-cells are disintegrated in one particular part 

 or organ, is not yet satisfactorily decided. Schult designated the 

 liver, and Kolliker the spleen, as the organ where this process is 

 effected. On the other hand, Grerlach and Schaffner regard the 

 spleen as the organ in which the corpuscles are formed. Scherer's 

 investigations confirm the idea of Kolliker. If there be a particu- 

 lar organ in which the corpuscles are formed, and another in which 

 they are disintegrated and dissolved which is still very doubtful, 

 however we should mention the liver as the former, and the spleen 

 as the latter (p. 170). 



Quantity of Blood in the Human Body. 

 Yery different estimates of the whole amount of blood have been 



