ness of less than one niitron, tlian it is in sectioned 

 tissue of 5 to 7 microns in thickness. Drying, 

 like tanning, seems to toughen the meml)ranes. 

 kack of stain penetration is well illustrated in 

 tlie use of Wright's stain on heterophils (figs. 

 154—167) where tlie micleus does not stain in 

 lliose portions that lie within the central part of 

 the cell. When the chai^acter of the membrane 

 is changed by a strong fixative, the stain pene- 

 trates readily and colors the chromatin brilliantly 

 (figs. 203—214). Another example is the baso- 

 ])hil nucleus, whieli often appears to be pale and 

 ghostlike with no evidence of chromatin or other 

 structure. This effect is in addition to the mask- 

 ing of the micleus by the basophilic granules 

 (figs. 190 and 191). In these illustrations, the 

 stained bodies simulating chromatin clumps 

 williin the l)oundary of each nucleus are actually 

 cytoplasmic basophilic granules; yet when the 

 membrane resistance is Ijroken down, the cell 

 proves to have a normal nucleus capable of in- 

 ternal staining (fig. 221). 



Dried immature cells appear to offer greater 

 resistance to penetration of stain than do mature 

 cells, and thus Wright's stain, which is able to 

 penetrate the memlnanes of normal circulating 

 cells, does not readily do so in the case of 

 precursor cells found in bone marrow, spleen, 

 tliymus, and other hematopoietic organs. On 

 the other hand, May-Griinwald Giemsa can pene- 

 trate inuuature cells quite well, with an occa- 

 sional exception (figs. 259, 281, and 334). Neo- 

 plastic blood cells are usually at various stages 

 of inunaturitv, and it is for this reason that fol- 

 lowing Wright's stain they often appear as baso- 

 philic rings with empty nuclei. A May-Griin- 

 wald Giemsa stain on these cells will generally 

 bring out the details of nuclear structure. Al- 

 though Emmel ( 1936) did not give the stain used 

 in his studies on hemocytolilastosis, many of the 

 figures he has depicted as degenerated cells are 

 identical in appearance with cells that have been 

 inadef|uately colored with Wright's stain. His 

 figure .3B is a good example. In this study such 

 conditions are regarded as defective technic, not 

 as degenerated cells. 



Jones (1948) discussed the problem of the 

 appearance of nuclei in cut sections versus dried 

 smears for embryo rat jjlood. and on most points 

 we are in agreement, except that he considers the 

 nuclear pattern as due to overlying mitochon- 

 dria: whereas, we recognize that cell organelles 



may play a part, yet believe that the pattern is 

 due chiefly to the arrangement of chromatin at the 

 nuclear meml)rane. 



The question can justifialily l^e raised. How 

 should the study of normal hematology be ap- 

 jnoached? In one book on human hematology 

 approximately the first hundred pages are de- 

 voted to the cytology of blast-cell types and their 

 derivatives. These figures form the basis of com- 

 parison for the subject matter of the body of the 

 book on blood diseases, yet approximately 85 

 jicrcent of the cells selected for illustration and 

 description in the section illustrating stages in 

 development of each blood-cell type came from 

 patients suffering from different types of leuke- 

 mias or infectious diseases. Only a few were 

 taken from normal, healthy individuals, and usu- 

 ally these were the mature stages of cell lines. 

 It is recognized that pathologic conditions often 

 reveal what cannot lie deciphered readily from 

 llie normal, where all processes of formation and 

 destruction of blood cell lines are in balance; yet 

 from our limited experience with pathologic 

 avian blood, undoubtedly we would have gone 

 astray had the picture of the normal been built 

 upon abnormal blood conditions. It was ob- 

 served for example, that heterophil myelocytes 

 found in circulating blood after irradiation were 

 slightly different in general appearance and cyto- 

 logic detail from those found in normal bone 

 marrow of the chicken. In leukemias as well as 

 in this example from irradiation, inunature cells 

 have been pushed into a new environment, and 

 thus two variables are operating, either of which 

 may be responsible for their slightly different ap- 

 pearance — (1) the chemical constitution of the 

 new environment and (2) the abnormal condi- 

 tions that produced them. 



Isaacs ( 1928) was dealing with essentially the 

 same problem when he noted that bone-marrow 

 cells and tumor cells stained more brilliantly 

 when mixed with blood senim than when im- 

 prints from these tissues were made directly on 

 the slide. 



As a side effect, the fact must not lje overlooked 

 that often disease conditions weaken and change 

 the permeability of the cell membrane; thus it 

 may well be that some of the differences we see 

 are merely a matter of degree derived from the 

 more effective penetration of the blood stains 

 used. Determination of the correct answer must 

 await further collection of data. 



