ERYTHROBLASTS IN THE PIG EMBRYO 145 



able, if not absolutely certain. To explain all the facts such 

 an envelope must be assumed to contain nucleoproteid, cholesterin 

 and lecithin" (p. 429); (see also Schafer '12). Albrecht ('03), 

 among the more recent investigators of the subject, has shown that 

 globules of this myelin substance have a tendency to become thin 

 at the center and thicker at the* rim in such a manner as to force 

 the fluid content to assume a disc form. One can readily verify 

 this by making an emulsion of a quantity of lecithin in water or 

 in a normal salt solution. Upon a microscopical examination 

 of a slide preparation of such a mixture, the globules of lecithin 

 can readily be seen becoming modified into flattened, biconcave 

 disc, and even approximately cup-shaped forms. The experi- 

 ments may be even more sj^rikingly performed, as suggested to 

 me by Dr. Bloor of the Department of Physiological Chemistry, 

 of the Washington University Medical School, by placing a small 

 quantity of lecithin upon a glass slide, adding a drop of water, 

 covering with a cover-glass and examining at once. Evidently, 

 then, the erythrocytic membrane includes elements which may 

 play an important role in the tendency toward the formation of 

 a biconcave disc or cup shape. Weidem-eich ('03, p. 478), has also 

 shown that this tendency may be evident even in the so-called 

 shadows remaining after the loss of the hemoglobin from the cor- 

 puscles through hemolysis. 



Returning to our original subject, on the basis of an intimate 

 correlation betweeni nuclear extrusion and the definitive form 

 of the corpuscle, it would appear necessary to assume that the 

 cell membrane plus its lipoid elements is either not present or 

 else does not become effective in the production of the definitive 

 form until after the extrusion of the nucleus. Indeed Albrecht 

 ('03), apparently appreciating this situation, has suggested that 

 the myelin substance is actually added to the surface of the cell 

 at the time of nuclear extrusion, for he states "es erscheint nicht 

 unwahrscheinlich dass gerade bei und nach der Ausstossung des 

 Kernes fettartige Substanz in grosser Menge an die Oberflache 

 der Zelle ausfliesst ; dadurch erkliirt sich nach Obigem der ange- 

 gebene Uebergang in die Glocken- und Dellenform nach der Kern- 

 ausstossung" (p. 19). But in contrast to this it may be pointed 



