chromophobic nuclear bands, and bird differ- 

 ences. In the set of slides, squashed cells were 

 rare but tliose that occurred did not show the type 

 of nuclear reaction illustrated in figure 58; in- 

 stead, the chromatin clumps remained discrete. 

 There was no indication of basicromatin lique- 

 faction and spread. The nucleus in figure 59, 

 before squashing, was probably similar to the 

 cell in figure 45, where a chromophobic l^and cut 

 across one end of the nucleus, and the cell in fig- 

 ure 60 was probably something like that shown 

 in figure 48. As the flattened nuclei with chromo- 

 phobic bands expanded, their structural details 

 became increasingly clear. Wlien one looks at 

 figures 59 and 60 with that thought in mind, it 

 becomes questionable whether "chromophobic" 

 is the best term to use in designating the clear 

 nuclear areas. The basichromatiu failed to re- 

 veal itself, not because it had lost its affinity for 

 nuclear stains but because it had actually disap- 

 peared. A study of chromophobic reactions in 

 lymphocytes (figs. 117-120) raises the same 



question. 



It is pertinent to ask whether such difi;erences 

 between birds in respect to nuclear reactions are 

 genetic or pathologic in origin. In any case, 

 these differences emphasize the fact that full use 

 has not yet been made of cytologic details that 

 could be applied as labels in various kinds of 

 experimental studies. 



A common artifact is the presence of vacuoles 

 in the cytoplasm (figs. 61-68). Two types are 

 illustrated in this series of drawings — non- 

 refractile vacuoles (figs. 61 and 63) and re- 

 fractile vacuoles (figs. 64^68). The former 

 type was found in slides from Laboratory No. 2 

 and the latter in slides from this Laboratory. 

 The cause of the nonrefractile vacuole is not 

 known, but it is undoubtedly a technic fault since 

 it was found on localized regions of the slides 

 with large expanses of normal erythrocytes in- 

 tervening. The vacuoles are fairly uniform in 

 size, perhaps widi some coalescence. They vary 

 from a few to many and may fill up the entire 

 cytosome. The nucleus was not affected by 

 vacuole formation in the cell body even when the 

 condition became extreme (fig. 63) . 



In an attempt to produce similar structures, 

 slides were overheated ; the only result obtained, 

 however, was a vacuole that was refractile. The 

 spheres may vary from very minute bodies (fig. 

 64) to relatively large ones (figs. 65-67) . They 



contain either air or moisture and the bul:)bles 

 often break through the cell wall as shown in 

 figure 65. An extreme condition is shown in 

 figure 68 where all the bubbles have left the cell 

 except one, which is in the process of extrusion, 

 and with the extrusion of the bubbles the cyto- 

 plasm is still vacuolated but not refractile. 

 Often the bubbles coalesce and form bizarre 

 shapes (figs. 66 and 67). They may form one 

 large vacuole with its margin intensely colored 

 (fig. 67), or a refractile, sausage-shaped mass, 

 or irregular bodies ( fig. 66) . The last named is 

 a common type and often appears in slides in 

 which there was no indication that too much heat 

 had been applied. The problem of the cause of 

 these artifacts still exists, and causes for their 

 production, other than heat, are not excluded. 

 Dawson (1931) has photographed erythrocytes 

 of Nectiuus that appear very similar to figure 67 

 and they occurred in fresh, unstained blood. In 

 conclusion he stated, "The vacuoles have been 

 interpreted as degenerative in nature, but no 

 specific cause for such changes in the erythro- 

 cytes has been discovered." 



Some artifacts produce appearances simulat- 

 ing cell abnormalities (figs. 69-72). The 

 cause of the magenta bodies found in the erythro- 

 cyte cytoplasm (figs. 70 and 71) and their pos- 

 sible confusion with Cabot's rings or intracellu- 

 lar parasites have already been discussed. A 

 red cell falling on top of another cell produces 

 a refractile curved line across the cell under- 

 neath and a concentric clear band of cytoplasm. 

 It is so obvious that the clear cytoplasmic line is 

 caused by pressure from the overlying cell that 

 no questions are raised, Init die same phenome- 

 non originating from a small granule or dust 

 particle falling on the surface of the cell before 

 it dries will often lead to erroneous interpreta- 

 tion. The tiny particle, if it is heavy enough to 

 depress the cell surface as it dries, will thin out 

 the underlying cytoplasmic layer and this will 

 look like a vacuole when the slide is stained. 

 Wliat one sees is a granule lying in the center of 

 a vacuole that appears to be located inside the 

 cytosome. Focusing does not help to determine 

 whether it is on top or inside, because the cell is 

 flattened to such an extent that its whole thick- 

 ness lies within the depdi of focus of the lens, and 

 even if focal levels could be separated it would 

 still look as if it were inside the cell, because the 

 particle has depressed the surface. 



40 



