ORIGIN OF COLORED BLOOD-CORPUSCLES. 103 



Based upon researches in cartilage and bone of birds, 

 Schoney, in 1876,* makes the following statements : 

 " E. Neumann t has denied the new formation of red blood- 

 corpuscles on the border of ossification of the cartilage. At the 

 same time he draws attention to Aeby, who already in 1858 

 suggested such a new formation. From the quotation of Aeby's 

 words, it follows that he only supposed the new formation on 

 the border of ossification, as his researches in this direction did 

 not yield positive results, whereas Heitzmann positively asserts 

 the fact of such a new formation. 



" E. Neumann's reasoning I cannot consider correct ; he, f. i., 

 could not understand that hasmatoblasts should stain with 

 carmine, while perfect red blood-corpuscles remain unstained. 

 Heitzmann claims that the haematoblasts are in a juvenile con- 

 dition of the protoplasm, from which, after certain changes have 

 taken place, red blood-corpuscles arise. Corpuscles may react 

 on being stained, in a different way, in their youth and old age. 



" E. Neumann, furthermore, makes a point of the absence 

 of nuclei in haematoblasts, assuming, as he does, that blood- 

 corpuscles in their juvenile condition must have nuclei, though 

 they are destitute of such later. My own researches may also 

 clear up this point. 



" E. Metschnikow f found in the impregnated and hatched germ 

 of fowl, at first nucleated, slightly colored, and later, nucleated, 

 distinctly colored, blood-corpuscles, and concluded that the latter 

 had originated from the former. This conclusion is not fully 

 justified, as it is possible that, from the same source, at first 

 slightly and afterward deeply colored blood-corpuscles may arise 

 and pass into the circulation without necessarily having directly 

 changed from one into the other. The same reasoning also holds 

 good for the blood-corpuscles of mammals. If at first nucleated 

 and afterward non-nucleated blood-corpuscles are visible, who is 

 willing to maintain that the latter have originated from the 

 former, and that each red blood-corpuscle must have had a stage 

 of nucleation ? 



* " Ueber den Ossificationsprocess bei Vogeln, und die NeuMldung von 

 rothen Blutkorperchen an der Ossificationsgrenze." Archiv fiir mikrosko- 

 pische Anatomie. Bd. xii. 



t Heitzmann's " Heematoblasten." Archiv fur mikroskopische Anatomie, 

 November, 1874. 



t " Zur Entwicklimgsgeschichte der rothen Blutkorperehen." Virchow's 

 Archiv, 41 Bd., 1867. 



