similar to those given by Hewitt (1940) in the 

 frontispiece. 



Richardson (1937) counted only those cells 

 as reticulocytes in which the granules completely 

 surrounded the nucleus. In his material he 

 found the normal count to be 7.8 percent with 

 a standard deviation of ±2.39. Robertson et al. 

 (1947) showed that chicks that had been de- 

 prived of folic acid for 4 weeks held a relatively 

 low percentage level of reticulocytes. One in- 

 jection of folic acid gave a sudden increase in 

 proportion of reticulocytes. Tlie peak of the 

 increase was reached on the sixth day. The per- 

 centage curve subsided to a normal level liy the 

 thirteenth day. 



An excellent review of the occurrence of retic- 

 ulocytes among various classes of vertebrates 

 and of the significance of the basophilic granu- 

 lations in these cells has been presented by Orten 

 (1934). His statement that sometimes nearly 

 all of the erythrocytes in pigeons, chickens, rep- 

 tiles, frogs, and fishes may be in the reticulocyte 

 stage, is based on observations made by Seyfarth 

 (1927). Graam (1934) found a similar result 

 in pigeons when she stained for 10 to 30 minutes, 

 but Seyfarth was aware of the fact that staining 

 for a long time damaged the cells. He found 

 that reticulocyte granules took up the stain in 

 a few seconds. Yet, in spite of the precaution 

 to keep the staining time short, sometimes he 

 obtained preparations from lower vertebrates 

 with a large proportion of the erythrocytes with 

 reticular granulations. From his colored illus- 

 trations of reticulocytes in the bone marrow and 

 blood of the fowl, he has included in the last 

 one or two steps of his developmental series, cells 

 which contained only a few granulations. Had 

 we included such cells in our studies as jjenig 

 reticulocytes, then we also would have been 

 forced to the point of view that practically all 

 erythrocytes in the circulating blood of either 

 chicks or adult birds were reticulocytes because, 

 as mentioned (last paragraph, p. 27), a pre- 

 cipitate was present over these slides and stain- 

 able granules existed both between the cells and 

 on the cells. Those on the cells resembled retic- 

 ular cell granulations. 



From our study of blood from normal adult 

 birds, the reticulocytes are extremely rare and 

 the possibility at least exists that the chicken 

 would be a better experimental animal than the 



pigeon for the types of study that in the past have 

 been applied to pigeons. 



These are all points that can be settled by 

 further study, but more significant at present 

 are the observations of Seyfarth (1927) that re- 

 ticulate granulations in mammalian blood are 

 not limited to die phases of erythrocyte matura- 

 tion that follow the extrusion of the normoblast 

 nucleus. By the use of reticulocyte staining 

 on cells from bone marrow, he found that these 

 granulations were present at very early stages 

 of development, when the cytoplasm was only a 

 narrow rim around the erythroblast nucleus. As 

 the nucleus became pycnotic at the late normo- 

 blast stage, the granules retained a perinuclear 

 position, forming a ring around the last of the 

 chromatin. After the chromatin had been en- 

 tirely discharged, the reticular granules (he calls 

 tliem substantia granulo-filamentosa) again scat- 

 tered throughout" the cytosome of the erythrocyte 

 and then gradually disappeared. 



An exactly comparable series of stages was 

 presented by Seyfarth from studies on the bone 

 marrow and blood of the chicken, except that 

 tlie nucleus was not eliminated from the cell. 

 In birds the reticular granulations almost entire- 

 ly fill the narrow rim of cytoplasm in the late 

 erythroblast or the early polychromatic erythro- 

 cyte and as the nucleus condenses, the granules 

 accompany its peripheral margin, thus leaving 

 the periphery of the cytosome free from granules. 

 There is no normoblast stage in birds at which 

 stage the nucleus is eliminated, but the behavior 

 of the reticular granules gives an indication when 

 this stage of development has been reached in 

 the maturation process of the avian reticulocyte. 

 This is indicated by the change from a condensed 

 band of reticular granulation around the nu- 

 cleus to a subsequent scattering of the granules 

 throughout the cytosome. Disappearance of the 

 granules is taking place at the same time. 



From these observations, it would appear that 

 the mature erythrocyte of the bird is homologous 

 to the mature erythrocyte of the mammal, and 

 not to the erythrolilast of man, as suggested by 

 Burckhardt (1912). 



The reticular granulations first appear m the 

 cell, immediately following the development of 

 hemoglobin in the cell (Seyfarth, 1927) . This 

 agrees with Dawson's data on the occurrence of 

 vftally stained granules in primary erythrocytes 



28 



