CHAPTER 1 



General Remarks and Definitions 



METHODS OF STUDY 



Blood cells may he studied in a variety of 

 ways. A perusal of the literature sometimes 

 gives the impression that one technical method is 

 far superior to another; hut actually each method 

 has its particular merit, and it is often found that 

 the advantages of a different approach compen- 

 sate for the shortcoming of the method that has 

 heen selected as the one generally to he followed. 



Some of the principal methods for studying 

 iilood and some of the advantages and disad- 

 vantages that have heen claimed for each method 

 are listed in table 1. The method chosen for 



this Atlas is the air-dried smear. It was chosen 

 for the reasons given in tahle 1 and hecause it is 

 the method most commonly used for routine blood 

 examination. 



Wright's stain was employed for the circu- 

 lating blood because it is the stain that is most 

 familiar to a large number of veterinarians and 

 research workers who are not specialists in the 

 field of blood. Other stains would undoubtedly 

 have made it possible to carry out certain phases 

 of the study with greater precision, but Wiight's 

 stain, in solution, keeps well, is easy to apply, 

 and may be procured from any medical or bio- 

 logical supply house. 



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



Metliod of study 

 KILLED CELLS 



Advantages 

 1. This meltiod permits a great variety of 

 technics to bring various components and 

 reactions of cells into view. Many technics 

 can he used ihat are sufficiently specific to 

 he niicrocheniical tests. 



1. Tissue, 

 stained. 



fixed, sectioned, and 



An example would he to drop a piece 

 of tissue such as embryo spleen in 

 Zenker ffjrmol, wash, rim through 

 alcohols, embed, section, and stain 

 in hematoxvlin and azure It eosin. 



2. Wet fixed smears. 



.\ lliiu smear of blood or other tissue 

 ci'lU on a slide that is dropped into 

 the fixative before it tlries. Usual 

 lerhniques from here on. 



Disadvantages 

 L Considerable alteration occurs in the tran- 

 sition from life to death; thus it becomes 

 difficult to <listinguish t)ctween structures 

 that existed in life and artifacts brought 

 about by death. 



1. Cells are fixed in a]>proxinialelv their 

 normal shape; that is, they are not flattened 

 as in dry smears. 



2. Maintains topographicrelationshipof cells 

 so that daughter cells and clusters of cells 

 having a connuon ancestor can be identified 

 by their proximity. 



3. Shows fixed cells of tissue as well as blood 

 cells. 



4. Some regard the cytological appearance 

 of fixed and sectioned blood cells as more 

 reliable than smears for distinguishing 

 differences. 



1. Cells are not killed as quickly in the center 

 of a mass of tissue as they are in a smear, so 

 that alterations in shape and organization 

 can occur. 



2. The method is time consimiing, especially 

 it a celloidin technic is employed. This im- 

 poses a greater limitation on a survey type of 

 study than does the smear metliod. 



3. Most investigators consider that minute 

 differences in nuclei and cytoplasm are not as 

 clearly differentiated in tissue sections as in 

 dry smears. 



1. Cells by this method duplicate the ap- 

 pearance tlie\ ha\'e in fixed preparations so 

 that cells studied by either method can be 

 readily compared. 



2. A fixing agent can be chosen that will 

 serve a particular purpose — i. e., the use of 

 methyl alcohol for preservation of granules 

 in blood and tissue basophils. 



3. Requires less time and equipment than 

 the fixed-tissue method. 



4. Cells usually not as severely flattened as 

 in dry fixed smears. 



1. Topographic relations with other cells 

 and tissues are lost. 



2. Cells do not show the delicate structural 

 and tinctorial gradations seen in dry smears. 



3. Has some practical disadvantages in the 

 field, since it involves carrying a nundier of 

 solutions. 



