clinical hematologists use the smear method ex- 

 tensively and, in general, hold to the polyphy- 

 letic theory. The statement that the theories are 

 determined by the technic used would, of course, 

 be too broad, but technic has certainly exerted 

 an influence that cannot be ignored. 



Much of the early basic concept of general 

 cell cytology was procured from sectioned mate- 

 rial, and the hundreds of textbook figures de- 

 picting the nucleus of the typical cell show its 

 internal structure only, the surface structure be- 

 ing practically ignored. Studying only the in- 

 ternal structure of a cell, or only the surface 

 structure, is comparable to gaining an impres- 

 sion of a house by noting the arrangement of 

 the rooms or by looking at it from the outside; 

 thus it is no wonder that hematologists seem so 

 far apart in their basic concepts when often a 

 particular school sees only one aspect of the 

 nucleus. 



The realization that the internal structure and 

 external surface of a nucleus can present en- 

 tirely different pictures came with the study of 

 the cytology of intranuclear inclusions produced 

 by viruses. In these cells the chromatin that 

 marginated did not disappear (Lucas and Herr- 

 mann, 1935), and the appearance of a thin line 

 against the nuclear membrane was not a line at 

 all but part of a reticulum just beneath tlie nu- 

 clear membrane (Lucas, 1940) ; that this was ac- 

 tually a reticulum could be seen only by focus- 

 ing on the membrane surface. Then, during de- 

 generation, the marginated chromatin aggre- 

 gated into larger and larger clumps. In cross- 

 section these appeared to be a string of closely 

 set beads, but in surface view they proved to be 

 rather widely spaced, irregular clumps, ar- 

 ranged at the interstices of a network. Still an- 

 other example illustrating that what appears as 



dots in cross section may be a network upon sur- 

 face view came from study of a prophase figure 

 of a liver cell containing a plasmosome nucleolus 

 (Lucas and Riser, 194.5, fig. 29). 



A cell that has been fixed and sectioned has 

 approximately its normal size and shape, where- 

 as a cell fixed by the smear method is spread out 

 and distorted into a very thin, flat disk. The 

 rough treatment might seem to he ample reason 

 for discarding the latter method as reliable pro- 

 cedure, but cells flattened in this way show many 

 cytological details that are never seen in a sec- 

 tioned cell. A series of three diagrams (fig. 1, 

 A, B, and C) illustrates what an observer sees 

 when viewing a sectioned nucleus. A, as com- 

 pared to a surface view of a flattened cell, C, and, 

 as already pointed out, this is a change from the 

 study of the interior of the nucleus to the surface 

 of the nucleus. These figures are merely dia- 

 grams but if A and C of figure 1 are compared 

 with the nuclear structures seen in section and 

 surface views, as illustrated in the detailed draw- 

 ings presented by Kirschbaum and Downey 

 (1937), the similarity is striking. 



In order to determine what happens to a cell 

 when it is spread on a slide, an experiment was 

 performed in which a slide was first coated with 

 a thin layer of celloidin and, when dry, a blood 

 smear was made in the normal manner on the 

 surface. The celloidin with the flattened cells 

 was peeled off and embedded in fluid celloidin, 

 hardened, and sectioned transversely to the blood 

 cells. Wlien these flattened cells were finally 

 located under the microscope, they were found to 

 be exceedingly thin, certainly no more than a 

 micron in thickness. The region of the nucleus 

 was scarcely thicker than that of the cytoplasm 

 alone. This means that the whole content of the 

 cell lies in the same level and, being thin, the 



Figure 1. 



A, B, C: Three stages in the shift of viewpoint from the 

 interior of the nucleus to the surface. 



A Cut section of a nucleus, showing nuclear membrane, 

 chromatin chimps, and a plasmosome nucleohis 

 (stippled disk). 



B A transitional step showing both interior and surface 

 views of the nucleus. 



C A flattened nucleus as it appears in a blood smear in 

 which the nuclear plattern is determined by the chro- 

 matin reticulum at the nuclear membrane. 



D, E: Scales for measuring cells. 



D Scale for measuring cells drawn at low magnification, 



1,.370X. 

 E Scale for measuring cells drawn at high magnification, 



2,470X. 



F, G: Appearance of hlood smears from chickens. 



F Smear from young birds, males and nonlaying females. 



G Smear from laying hens. Clear areas due to droplets of 



fat that flatten and spread when the smear is made. 



