FORMATION OF BLOOD-CELLS. 273 



the general composition of the blood and the metamorphosis of the 

 animal tissues. 



With reference to the chemical phenomena accompanying the 

 morphological transition of colourless into coloured cells, we only 

 know that hsematin is gradually developed within them, and hence 

 we must content ourselves with a brief reference to the views held 

 by recent physiologists regarding the morphological process; 

 omitting all notice of the older hypotheses. 



The once generally accepted view that the red blood-corpuscles 

 are formed from the nuclei of the lymph- and chyle-corpuscles, 

 by the disappearance of their walls, has found no advocates in 

 recent times. H. M uller, on the other hand, adopts the view that the 

 colourless cells are directly converted into the red blood-corpuscles, 

 and believes that the small lymph-corpuscles which occur in the 

 thoracic duct owe their origin to the loss of their fluid granular con- 

 tents, and that thus the capsule approximates more closely to the 

 nucleus, whilst all their contents disappear so entirely in the blood, 

 that the membrane comes in contact with, and constitutes the actual 

 investment of the nucleus. The corpuscle is then flattened in an 

 analogous manner to the nucleus, and appears concave, while the 

 nucleated vesicle imbibes red pigment and thus becomes formed into 

 a perfect blood-corpuscle. The chemical behaviour of the cell- 

 wall of the corpuscles seems however opposed to this view, and 

 there are many other reasons unfavourable to its adoption. 



According to Kolliker, the most probable view is that which 

 assumes that the smaller kind of chyle-corpuscles is converted by 

 the disappearance of the nucleus and the absorption of pigment into 

 the true blood-corpuscle ; he advances the following grounds in 

 support of this view : (1) The similarity of size in the smaller chyle- 

 corpuscles of the thoracic duct and the red blood-corpuscles ; (2) the 

 perfectly identical behaviour of the capsule of these chyle-corpuscles 

 and of the wall of the blood-discs towards physical and chemical 

 influences ; (3) the faintly yellow colour of these chyle-corpuscles 

 with an entirely colourless nucleus ; (4) the flattening, although in 

 a less degree than in fully developed blood-corpuscles ; and (5) the 

 nuclei of the smaller chyle-corpuscles are entirely different from 

 the blood-corpuscles. 



To these three theories regarding the transition of colourless 

 into coloured corpuscles Gerlach has added a fourth, which is 

 principally founded on the occurrence of cells containing blood- 

 corpuscles in the Malpighian corpuscles of the spleen and in 

 the liver of the embryo. According to him, the coloured blood- 



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