ERYTHROBLASTS IN THE PIG EMBRYO 173 



on Anemia, ' ' the investigations of the last ten years have failed to 



reconcile the champions of these doctrines Suffice it 



to mention that the names of E. Albrecht, Howell, M. Heiden- 

 hain, Vd. Stricht, and Jiinger have appeared in support of Rind- 

 fleisch; while Massloff and Naegeli have recently taken up the 

 cudgels for Neumann and Kolliker" (p. 73). Since, however, the 

 greater number of recent investigators, including Jolly, Maximow 

 and Weidenreich incline toward the view of nuclear extrusion, 

 some of the evidence for the latter conclusion may accordingly 

 be here briefly discussed, confining our attentions chiefly to con- 

 ditions in the embryo. 



The following facts are among those which have been advanced 

 as evidence for nuclear extrusion. First may be mentioned the 

 presence of free nuclei in the circulation. Granting that a given 

 free nucleus is erythrocytic in origin, for the conclusion that it 

 must have originated by nuclear extrusion, two other alterna- 

 tives have already been presented, namely, that the nucleus under 

 consideration could have separated from the erythroblast by a 

 cytoplasmic constriction so close to the nucleus as to leave it 

 practically, if not entirely, free from any surrounding cytoplasm, 

 or that the nucleus plus a small quantity of cytoplasm as originally 

 separated from the parent cell had subsequently lost this cyto- 

 plasm by fragmentation. 



A second argument for nuclear extrusion has been based upon ' 

 the occurrence of free erythrocytic nuclei ingested by phagocytic 

 cells. Concerning this point it is readily appreciated that if the 

 objections just raised in connection with the subject of nuclei free 

 in the circulation are valid, they apply with equal force to the in- 

 terpretation of the ingested nuclei found in the phagocytes. Fur- 

 thermore it is not to be overlooked that the entire erythroblast 

 as well as free nuclei may be phagocytized, as has been described 

 and figured by Maximow ('09) for the rabbit embryo (pp. 480 

 and 545) . The writer has also observed the same phenomenon in 

 phagocytic cells of the pig embryo. A dissolution or digestion of 

 the cytoplasm before that of the nucleus in such an ingested cor- 

 puscle would leave an uncertainty as to whether a given nuclear 

 inclusion represented a previously cytoplasmic free nucleus. 



