Interpretation of the loss of rods is sometimes 

 influenced by the type of problem involved. 

 Hewitt (1940) attributes this loss to degenera- 

 tion or phagocytosis due to the malarial parasite. 

 Difficulty in the identification of eosinophils and 

 heterophils is not limited to the older literature; 

 for example, Diesem (1956) found it difficult 

 to separate these two cell types, and combined 

 them in his cell counts. 



The most recent opinion on the subject of rod 

 degradation has been expressed by Dr. Hamre 

 (personal communication). The opinion is that 

 the rods themselves remain unchanged when acted 

 upon by various stains and aqueous solutions but 

 that the capacity of the rod substances to absorb 

 the stain does change, and that if Wright-Giemsa 

 is used as he has modified it (the technic he rec- 

 ommends is given on p. 230) rods will always 

 stain and each rod will contain a central granule. 



One additional cellular defect remains to 

 be described — squashed cells. Squashed or 

 smudged heterophils are probably the easiest 

 cells to recognize because the specific cellular in- 

 clusions are preserved. Squashing takes place 

 at the time the smear is made; yet the same vari- 

 ability is to be found in the rods broken out of 

 the cell as was found in the intact cell (figs. 175 

 and 176). Figure 175 shows rods without cen- 

 tral granules and figure 176 shows central gran- 

 ules with dissolved and almost completely faded 

 rods. These were taken from different jjirds but 

 ])oth smears were made the same day. The birds 

 were exactly the same age and the slides were 

 stained together. Both cells show many fine 

 magenta-colored granules, partly among the 

 broken fragments of the cell but mostly surround- 

 ing the cell. These small, darkly stained bodies 

 are senmi granules. Something is liberated 

 from the broken cell that acts as a mordant on 

 the serum granules and causes those in the imme- 

 diate vicinity to take the stain. As may be seen 

 from figure 176 their color and size differ from 

 even the smallest of the central granules of the 

 rods. The central granules show a variability in 

 size among themselves similar to that found in 

 the intact cell. 



EOSINOPHILS 



The fact that both heterophils and eosinophils 

 stain with eosin has led to the use of numerous 



terms for designating tliese two cell types, such 

 as "rod eosinophils," "granular eosinophils," 

 "pseudoeosinophils," and "true eosinophils." 

 Some have reversed the last two terms so that 

 "true eosinophil" applies to the heterophils. For 

 this reason, the use of "true" and "pseudo" can 

 lead to confusion. The terms "rod" and "gran- 

 ular" are not good either because rods often 

 change to spheres. Therefore, the terms "heter- 

 ophil" and "eosinophil" have been chosen. 

 These have the added advantage that the cells 

 are each designated by one word instead of two. 

 The eosinophil of birds is homologous with the 

 cell receiving the same name in other classes of 

 vertebrates. 



ISornial mature eosinophils (figs. 177— 

 183) 



The eosinophil shows a rather wide range in 

 size; some are large, like figures 177-180, and 

 some small, like figures 181-183. Usually they 

 are about the size shown in figure 177. The 

 range for size (fig. 197) is shown by a frequency 

 distribution curve in which there is a minimum 

 of a little over 4/u to slightly over llyu. The 

 average size of 7.3;U is approximately 1 micron 

 less than for heterophils or basophils, and prob- 

 ably was brought about by the occurrence of 

 small eosinophils in circulating blood ; whereas, 

 cells of the size shown in figures 181-183 are 

 rare for heterophils or basophils. The cell is 

 nearly round as may be seen from the figures. 



The cytoplasm stains a pale, clear blue color, 

 which, of course, shows best when the granules 

 are not crowded together. The granules are 

 often crowded and there is not much cytoplasm 

 to be seen ; yet the background blue color is one 

 of the best means of separating the two types of 

 eosin-staining cells when the rods of heterophils 

 have been degraded to granules. The blue- 

 staining ground substance is readily apparent 

 among the granules of large eosinophils, but the 

 blue color is often obscured in small cells. 

 Small cells, such as those shown in figures 

 181-183, are relatively rare. Their identifica- 

 tion is aided by the strong affinity of the nucleus 

 for stain. 



There is some variation in the structures of the 

 granules. Often they appear as homogeneous 

 bodies, Ijut sometimes when they are larger and 



89 



