ERYTHROBLASTS IN THE PIG EMBRYO 141 



of the cell body is presented (fig, 21, c), the turning is then com- 

 pleted and the cell again lies flat upon the slide but with the pre- 

 viously lower face of the disc now uppermost (fig. 21, d). In 

 other words, during the entire process of rotation the side of the 

 disc containing the nucleus tends to remain nearest the slide as if 

 loaded, so that the cell body appears to rotate with the nucleated 

 portion as a more or less fixed point, indicating that this part of 

 the disc is the heavier portion of the erythroblast. This experi- 

 ment was performed repeatedly with such uniform results that it 

 was found almost impossible to obtain, for the purpose of making 

 a camera lucida drawing, a satisfactory profile view of the cell with 

 the nucleus uppermost. Similar observations were made on the 

 living vessels where the erythroblasts, freely suspended in the 

 plasma and not disturbed by adjacent cells, always tended to 

 swing with the nuclear pole undermost. The same phenomenon is 

 also most strikingly demonstrated in erythroblasts from which 

 the hemoglobin has been removed by hemolysis. In this case 

 also the nucleus remains suspended on the under side of the so- 

 called shadow, 



4. UNEQUAL REACTION OF CYTOPLASMIC AND NUCLEAR POLES TO 



OSMOTIC CHANGES 



Figure 22 represents an erythroblast from the blood of a 28 mm. 

 pig embryo kept in Ringer's solution for about forty-eight hours, 

 and figure 45, a similar cell from a four-day autoplastic culture of 

 a 33 mm. pig embryo. These erythi'oblasts do not show any 

 special evidence of degenerative change other than a swelling of 

 the cell body due, presumably, to the absorption of a quantity of 

 water, so that the previously disc-shaped corpuscle has assumed a 

 rounded appearance. The important point here is that this re- 

 action has not manifested itself uniformly throughout the whole 

 cell body. This is not so evident when the cell is lying flat and 

 undisturbed as in a; but when it is rotated so as to present a pro- 

 file view, as in h, it will be observed that the swelling reaction has 

 taken place largely, if not entirely, in that region of the disc oppo- 

 site the nucleus, which may be conveniently designated as the 



