mal; yet the average index for the 4 that went 

 to the termination date and were fonnd grossly 

 negative was 2.65. Perhaps this is a more nearly 

 normal index than the lower value. A group of 

 chickens known to be free from the agent of lym- 

 phomatosis and other diseases is needed in order 

 to arrive at a set of normal standard blood values. 

 The question also arises, Are the birds that are 

 destined to develop grossly visible tumors in- 

 fected and fighting against the disease during the 

 several hundred days before neoplasia appears? 

 Before leaving the subject of the normal hetero- 

 phil, the fact should be mentioned that the French 

 veterinarian, Lesbouyries, (1941) described a 

 sixth type of white blood cell in chickens. He 

 listed a neutrophil in addition to a heterophil. In 

 his descriptions tliey are not synonymous. His 

 sixth cell is the type shown in figure 165 and it 

 does resemble superficially a mammalian neutro- 

 phil. Our own studies have shown it to be a het- 

 erophil from which the rods (without granules) 

 have dissolved, and there is no justification for 

 giving it a different name and creating a separate 

 class for it. Breusch (1928) listed 4 types of 

 granulocytes — eosinophilic leukocytes, ampho- 

 philic or pseudoeosinophilic leukocytes, baso- 

 philic leukocytes, and neutrophilic leukocytes — 

 but descriljed only the first 3, and includes only 

 these 3 in his tables of differential counts. The 

 application of terminology whereby heterophils 

 and eosinophils are correctly identified has not 

 been a simple matter. Magath and Higgins 

 (1934) have listed the various synonyms that 

 have been used from 1880 to 1931. Even sepa- 

 ration of these cells on the basis of those with 

 eosinophilic rods and those with eosinophilic 

 graiuiles leads to difficulty in identifying these 2 

 cell types in ducks (see p. 207). Loewenthal 

 (1930) also found what he called neutrophiloid 

 cells, which in his opinion were derived from 

 rods by a process of dedifferentiation; he sug- 

 gested that in the course of evolution it was 

 this type of cell that produced the mammalian 

 neutrophil. 



Developmental stages found in circulating 

 blood (figs. 168-173) 



Immature cells of the heterophil series are rare 

 in normal blood, but probably not more so than 

 are the immature stages of red cells when the 

 difference in relative numbers is taken into ac- 



count. If the heterophil count is recovering after 

 destructive irradiation, the immature heterophils 

 may be quite numerous. 



A granuloblast found in the circulating blood 

 is shown in figure 168. There may be some 

 question of whether it is destined to be a heter- 

 ophil or a basophil, but the large size of the cell, 

 the rim of basophilic cytoplasm broken by many 

 mitochondrial spaces, and the uniform reticular 

 pattern of the nucleus, all identify it as a blast 

 cell. When compared with the granuloblasts of 

 figures 330, 1 and 2, 366, and 367, little doubt 

 remains as to its identification as a granuloblast. 



The metagranuloblast stage of development 

 has not been seen as yet in the circulating blood, 

 ]:)ut is found in bone marrow ( figs. 368 and 369) . 



Four examples of promyelocytes (figs. 169- 

 1 72 ) have been illustrated. The nuclear bound- 

 ary in the earlier phase of development (figs. 169 

 and 170) is even less distinct than in the bone 

 marrow, and the number and density of magenta 

 rings and granules are greater. Figures 171 and 

 1 72 are not good examples of late promyelocytes, 

 because the contents of the vacuoles did not take 

 the stain. It is assumed that tlie same stage, had 

 it been taken from the bone marrow, would have 

 looked like figures 370-372. 



These immature heterophils in circulating 

 blood have a different appearance from those in 

 bone marrow. Perhaps this is due to the fact 

 that different stains were used in tlie two situa- 

 tions, or it may be due to the effects of these en- 

 vironments on the penetrability or selectivity of 

 the stains. Whatever the cause, the difference in 

 appearance should be kept in mind and not be al- 

 lowed to hamper identification. 



A typical mesomyelocyte (fig. 173) has less 

 than half of the definitive granules. Many of 

 the precursor orange spheres have attained a 

 dense coloration but none of them have elongated 

 as in figure 373. Two sizes of granules are 

 present, and there is a possibility that the small 

 ones become the central bodies for the rods that 

 develop out of the large ones. The carryover of 

 magenta rings and granules from the early to 

 the late stages sometimes occurs as it has in figure 

 173. The whole process of myelopoiesis will 

 not be discussed at this time since a rather critical 

 and detailed comparison, which is presented 

 later, is necessary in order to relate what is found 

 in birds to the named stages given for mammals. 

 See also the discussion by Lucas (1959). 



86 



