SPECIES IDENTITY OF NUCLEUS-PLASMA NORM 471 



out with the end sections of both nucleus and plasma apparently 

 complete and without a trace of either element in the immediately 

 adjoining sections in the four possible chances (Cells 8 and 12). 

 Since a partial section estimated as a full one not only makes an 

 appreciable difference in the weight but also makes a dispropor- 

 tionate difference as regards mass relations on account of the 

 much smaller size of the nucleus, it was obviously necessary to 

 attempt an approximation of the actual thickness. The reading 

 of the optical section from the scale on the Zeiss fine adjustment 

 screwhead helped materially, but no attempt at closer accuracy 

 was made than to judge whether the sections went one-fourth, 

 one-half, or three-fourths through. The wax duplicate was 

 trimmed accordingly. 



2. The necessity of making certain allowances. In general, 

 the theory of wax reconstruction that the straight edges of the 

 wax layers when smoothed down will conform to the sloping 

 edge of the prototype itself and that thus the surface will be 

 equalized evidently applies to such small objects as the individual 

 cells in question. However, it is equally evident that in places 

 it does not. Without going into detail, for the cases where it 

 fails would be obvious to any observer, only two instances will 

 be mentioned. Where a polar section is of the same area as 

 the next adjoining, which frequently occurs, in the nucleus 

 particularly, it is plain that since the outer surface of this polar 

 section is spheroidal, a plate with a straight edge gives substance 

 in excess. Again in the nucleus it occurs not infrequently in 

 polar sections that the boundaries of both its surfaces appear 

 on focusing, one very decidedly smaller than the other, or there 

 may be definite indication of sloping that a straight edge will not 

 account for. In these and other instances where the form of 

 the reconstruction supported the microscopic indication, allow- 

 ance was made, usually reciprocal, either to supply a deficiency or 

 to remove an excess. However, such modifications were avoided 

 except on very definite indications. 



The accuracy, therefore, in regard to these two factors rests 

 upon personal judgment. Most fortunately, however, the 

 success in obtaining sections at one micron lessens their impor- 



