Table 1. — Advantages and disadvantages of various methods that have been used to study blood 



cells — Continued 



Method of study 

 1. \ ital staining. 



Afellivlene blue (vital), neutral red, 

 Janus green H. and brilliant cresyl 

 bine are examples of vital dves that 

 have been used extensively. 



Advantages 



1. Motility and reactivity can be correlated 

 with cell cytology. 



2. Gives a sharper separation of lympho- 

 cytes and monocytes tlian with other tech- 

 nics. 



3. Some degenerative reactions may be use- 

 fnl, such as the occurrence of vacuolization 

 in granidocytes that appear 30 to W niiimles 

 after the preparation is made. 



Disadtantages 



1. Vital dyes used in studies of this sort are 

 usually slightly toxic. 



2. Clean slides are very important in supra- 

 vital technics and may refpiire 3 to 4 weeks 

 to prepare |>roperly. Thus this teclmic can- 

 not be set up on short notice. 



3. Fails to show variations in cytoplasmic 

 basophiUa and in nuclear details as \\ell as 

 they are shown in drv smears. 



1. Degenerative processes inherent in vital 

 preparations are a limiting factor in I he num- 

 ber of slides that may be studied at one lime; 

 thus, weekK c-(kuUs on 23 birds wouhl be 

 more of a task by this method than by using 

 drv smears. 



2. Darkfield illumination. 



A microscopic technic (usually 

 with a special condenser) whereby 

 light enters the field at such a wide 

 angle that the field appears black 

 except where the light strikes a 

 particle and bends upward towartl 

 the observer. 



1. Often reveals extremely delicate jiroto- 

 plasmic ]>rocesses such as filanicnls of 

 erythrocytes and the undulating membrane 

 of monocytes. 



2. t seful for study of formed structures 

 within the cell and movements of cells 

 without the introduction of toxic agents. 



1. Not adaptable to routine study of cells 

 or to making differential C4)unts. 



2. The reflected light gives a dislorleil im- 

 pression of the real size of lines and dots. 



3. Phase microscopy. 



A microscopic technic that utilizes 

 some principles of darkfield. inter- 

 ference phenomena, and differences 

 in refractive indices of various 

 materials within the cell. 



1. Has advantages of vital staining in 

 showing movements and the existence of 

 [ireformed structures such as granules and 

 mitochondria without the disadvantage of 

 introducing toxic dves. 



2. Reveals almost as wide a variety of 

 structures as may be shown in fixed and 

 stained preparations. 



3. Excellent for exposing technic artifacts 

 induced by killing and staining cells. 



]. Does not get the full range of tinctorial 

 variations obtained in stained slides. 



Wright's stain is often capricious when ap- 

 plied to circulating Llood of embryos, to bone 

 marrow, to spleen, and to pathological blood that 

 contains blast cells. The chief objection is its 

 frequent failure to penetrate adequately and 

 stain the nuclei; the nuclei remain pale blue and 

 seemingly structureless, but close examination 

 under oil immersion reveals that the structures 

 are actually present, and duplicate slides stained 

 with May-Griinwald Giemsa demonstrate that 

 the lack of staining is not due to degeneration 

 of the cell. Additional conunents on Wright's 

 stain are given in chapter 7, page 228. May- 

 Griinwald Giemsa has been used routinely in this 

 Laboratorv for a mmiljer of vears and in this 



study has been applied to all embryonic blood 

 and to impression smears of embryonic and adult 

 hematopoietic tissues. 



The great variability of approaches to 

 the study of blood-cell morphology has been 

 brought out in table 1, and it is quite evident 

 that no one method has all the advantages with 

 no disadvantages. The numerous theories of 

 blood-cell genesis and developmental potentiali- 

 ties often have been associated witli a particular 

 technic; for example, the Maximow school de- 

 veloped and used celloidin on fixed and cut sec- 

 tions and arrived at the unitarian theory of 

 hemocytogenesis, and many proponents of this 

 theorv continue with the same technics. The 



