not so crowded, the structure of each granule is 

 revealed. It is made up of 3 or 4 smaller bodies 

 held together in a ring. This is shown especially 

 well in figure 177. The small granules that 

 make up the ring give it an angular contour and 

 in the center is a clear space. Sometimes one 

 may have an impression of a clear space in the 

 center of the sphere (fig. 180) and yet the indi- 

 vidual particles that go to make up the ring can- 

 not be separated. 



A knowledge of the detailed structure of the 

 eosinophil granule (or ring) in the chicken is 

 necessary for the identification of the eosinophil 

 in various species of wild birds, especially the 

 ducks. The space may be responsible for the 

 general report that the eosinophil granules are re- 

 fractile. In formalin-fixed cells that are stained 

 with phloxine and floated on a slide, as they are 

 in the counting chamber when Wiseman's method 

 has been used in preparing tlie material, they can 

 readily be distinguished from heterophils by 

 their strong refractility. Had these differences 

 been observed by Lundquist and Hedlung ( 1925) 

 they probably would not have concluded that 

 these two eosin-staining cells belong to the same 

 type. 



Usually, granules are uniformly stained but 

 it is fairly common, especially in medium to 

 large cells, to find that some of the granules stain 

 faintly, as shown in figures 178 and 179. Quite 

 often in association with this variation there are 



differences in concentration of granules in dif- 

 ferent parts of the cell, as shown in the two exam- 

 ples. It may be that these deficiencies represent 

 immaturity of the cell; yet the fact that there are 

 four nuclear lobes is evidence that the cell in fig- 

 ure 179 is not an immature cell; perhaps the 

 cytoplasm continued to increase in volume after 

 the process of granule formation had ceased. 

 Further discussion of the problem of variation in 

 the size and arrangement of eosinophil granules 

 appears later (ch. 6 and fig. 411). 



One characteristic of the granules in the eosin- 

 ophils that aids in separating them from hetero- 

 phils containing granules is the impei-viousness 

 to aqueous solutions; the granules of the eosino- 

 phil are never affected in the chicken and the 

 same difference is shown following Petrunkevitch 

 No. 2 fixation (compare figs. 203 and 21.5). 



The nucleus always stains well in the eosino- 

 phil. Except for the masking of lobes by the 

 granules, it would be possible to count the nuclei 

 quite accurately. No cell with more than 4 nu- 

 clear lobes has been illustrated, and the data for 

 eosinophils in table 6, based on 142 cells counted, 

 also indicate that an eosinophil with 5 or more 

 loJjes would lie rare in the chicken. The Arneth 

 index for eosinophils, 1.97, is lower than for 

 heterophils. 



To point up the differences between these two 

 cell types for purposes of identification, table 8 

 was prepared. 



Table 8. — Characteristics of heterophils and eosinophils 



Characteristic Heterophil Eosinophil 



Cell size Usually a relatively small range of variation in Wide range in size but usually not in the same 



circulating blood but a large range of variation slide, 

 in the bone marrow. 



Cytoplasm When rods are well formed the cytoplasm is The cytoplasm maintains a pale blue background 



colorless. If there is any degradation of rods to color for the red-staining granules. Only rarely 



spheres, the cytoplasm is tinged with the is there an exception to this, 

 eosinophilic material. 



Specific granules Contain eosinophilic rods that may be long and Contain eosinophilic bodies that are uniform m 



narrow, or short and plum]), or even spherical, size in the same cell and usually uniformly dis- 

 Rods disintegrate in aqueous solutions and the tributed. Eosinophilic bodies may be homo- 

 central body may be all thai remains. Central geneous spheres or rings, often with 4 granules in 

 bodies are variable in number and size; they the ring, or scattered separate small granules, 

 may be absent or may be represented by a Resistant to aqueous solutions. In some species 

 vacuole. the rings may be flattened and elongated to give 



the superficial appearance of a rod. 



Nuclear lobes . 



Nuclear staining . 



The average Arneth index is 2.44 or higher for The average Arneth index is slightly less than 

 chickens. 2.00. Cells with class V nuclei are rare in chick- 



ens, if they exist at all. 



Wright's stain usually fails to stain the nucleus Wright's stain shows a strong affinity for the 

 completely or well. nucleus and brings out the details of chromatin 



pattern. 



90 



