THE BLOOD AND THE LYMPH. 345 



into coloured cells. Where and how this takes place, no one 

 has seen ; and notwithstanding all the trouble and care that I 

 have devoted to the subject, I have never noticed a nucleated 

 coloured blood-cell in the adult. The only thing of the sort 

 that I have met with, has been this, that in the pulmonary 

 veins, and occasionally also in other blood, the smaller lymph- 

 corpuscles were in many instances pretty distinctly coloured, 

 much more so than in the thoracic duct, so that, except from 

 their faintly granular aspect, they were scarcely distinguishable 

 from the true blood-cells lying on their flat side; and the 

 more so, because they contained somewhat smaller nuclei than 

 elsewhere ; but even this circumstance is insufficient to decide 

 the question. The following points, however, may be adduced 

 as presenting very important analogies : 1. that in all the 

 lower Vertebrata, very distinctly for instance in the Amphibia, 

 even in adult animals, the origination of nucleated blood-cells 

 from the lymph-corpuscles may be observed; and 2. that, in 

 the human embryo also, the formation of the coloured blood- 

 globules from colourless cells very closely resembling the lymph- 

 corpuscles, has been demonstrated by me in the most decisive 

 way. If to this it be added, that there is not the slightest 

 evidence of an independent, or other kind of origination of 

 blood-cells, it may perhaps be considered quite justifiable if 

 I maintain their origination from the lymph-corpuscles; and, 

 in order to explain the reason why the transition itself has not 

 yet been observed, if I broach the supposition that it may 

 take place too rapidly to be in any way obvious with our 

 means of observation. 



Although in what has been said, I express myself in favour 

 of the formation of the red blood-cells from the elements of 

 the lymph and of the chyle, I would by no means assert that 

 all the elements of those fluids become blood-cells at every 

 period of post-embryonic life. The microscopical investigation 

 of the blood would rather show, that they invariably contain a 

 certain number of larger pale cells with several nuclei, or a 

 single nucleus disintegrated by acetic acid, of which, although 

 they are certainly derived from the chyle, or are metamor- 

 phosed elements of it, it is perhaps impossible to suppose that 

 they ever become blood -cells. This being established, it is a 

 question whether the change of the blood-cells, their formation 



