THE BLOOD. 161 



puscles of the blood (especially the smaller) may be regarded as 

 merely a transitional stage of development of the red corpuscles. 

 The idea of Kolliker, however, that they are not all converted into 

 the colored corpuscles in the human body, is confirmed by com- 

 parative histology ; since in all the white-blooded animals they are 

 arrested in their development, and form no colored corpuscles, 

 though they are in some animals quite abundant. 



The manner in which the red corpuscles are developed from 

 those under consideration will be specified in the following section 

 (p. 168). But it should be here added that even in the white- blooded 

 animals they cannot, during their development and their metamor- 

 phosis, be without influence on the composition of the blood, and 

 thus, directly or indirectly, on the development and the metamor- 

 phosis of the tissues. Besides, they will incidentally secure a 

 patulous condition of the minute vessels, and thus subserve the 

 circulation of the liquor sanguinis in these species. The former 

 remark may also be applied to the human cytoid corpuscles, since 

 they are living cells manifesting an active interchange of matter 

 with the blood- plasma. 



To them, therefore, as well as to the fibrine, the blood owes its 

 vitality. Those who maintain that fibrine is the pabulum of all the 

 tissues, have suggested that the colorless corpuscles elaborate fibrine 

 from the albumen in the blood. This is quite improbable; for 

 though the amount of fibrine and the number of colorless corpuscles 

 are sometimes simultaneously increased (as in inflammation), there 

 are no grounds for the opinion that these cells contain any fibrine 

 at all. 1 In leucaemia, also, the cells are abnormally numerous 

 (even one to three red blood-corpuscles), while the fibrine is not 

 increased ; and the same is also true of the blood of young and 

 growing animals. They are, therefore, to be regarded as entirely 

 independent, histologically, of fibrine, and their increase or dimi- 

 nution must be attributed to causes acting independently upon 

 them. "Wherever growth is going on, cytoid corpuscles appear 

 e. g. in new formations, reparative or otherwise, or in the original 

 development of the tissues and it might be expected that they 

 would be developed rapidly in the blood also of young animals, as 

 one of its normal constituents ; its metamorphosis being rapid, as 



1 An increase of fibrine in the blood is perhaps always attended by an increase 

 of white corpuscles, but the converse of this does not hold. 

 11 



