720 SPECIAL HISTOLOGY. 



two, so numerous in the hepatic blood, are wholly wanting in the rest 

 of that fluid. 



The origination of the blood-globules after birth and in the adult, 

 notwithstanding the great pains specially devoted to this point, still 

 remains one of the most obscure parts in the history of the blood-cells ; 

 in my opinion, however, the notion which assumes that the red blood- 

 cells proceed from the smaller chyle-corpuscles, which lose their nuclei, 

 become flattened, and have hematin produced in them, is the one most 

 deserving of credit. These cells are about of the same size as the 

 blood-globules, or even rather smaller, have the same kind of membrane 

 as the latter, are flattened, and not unfrequently of a faint yellow 

 color, and consequently may, as we see in the colorless blood-cells of 

 the embryo, pass without any considerable change into colored 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 colored blood-cell in the adult. The only 

 thing of the sort that I have met with, has been this, that in the pul- 

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

 corpuscles were in many instances pretty distinctly colored, 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 some- 

 what 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 colored blood-globules from colorless 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 favor of the for- 

 mation 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 micro- 

 scopical investigation of the blood would rather show, that they invari- 

 ably 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 metamorphosed elements of 



