132 VICTOR E. EMMEL 



It then remained to account for the spherical appearance of 

 these cells as seen in slide preparations and hanging drops. If 

 these were really more or less disc form, it should be possible to 

 determine this point by turning the cells over so as to view all sides 

 of a given cell. For this purpose a drop of fresh blood was placed 

 on a carefully cleaned slide, covered with a clean rectangular cover 

 glass, and the rim of the cover glass sealed with vaseline. The 

 corners of the cover glasses used for this purpose had beein 

 previously heated and the tips bent down slightly, thus forming 

 sufficient support to prevent pressure of the cover glass upon 

 the blood cells. Upon studying such preparations it was found 

 that by means of a very slight pressure produced with a pencil 

 tip upon the somewhat flexible cover glass, in the vicinity of the 

 microscopic field, the cells could be gently rolled about and turned 

 over almost at will. Selecting large nucleated erythroblasts which 

 appeared typically spherical in form, they were then manipulated 

 in the above manner and it was discovered that in the majority 

 of cases they could be turned so as to present a narrow profile 

 which varied from an almost perfect biconcave disc to a more or 

 less concave-convex or cup-shaped form (figs. 21, 41, 43 and 44). 

 It was very difficult to keep these cells standing on edge for more 

 than a moment on account of their constant tendency to turn over 

 and lie flat upon the slide. This tendency in orientation accounts 

 for the appearance of these cells as studied in dried or fixed cover- 

 glass preparations, or even in hanging drops of fresh blood, for 

 no sooner has the drop of blood been placed on the slide or cover- 

 glass than the erythroblasts immediately orient themselves so 

 as to lie flat upon the horizontal surface. In this position the 

 appearance is very deceptive, for the flattened or disced contour 

 in most cases can scarcely, if at all, be detected in the optical 

 sections obtained by focussing, and consequently the observer 

 may be readily led to the conclusion that they are spherical. It 

 is interesting to note that Engel ('99) recognized a possible flatten- 

 ing of the younger erythroblasts (metrocytes I) in his dried prep- 

 arations, but that he regarded this as the result of fixation and not 

 a normal form is indicated in the following statement, made in 

 connection with his observation that some of the erythroblasts 



