"This maturation of the fowl's blood takes a 

 shorter time than the equivalent development 

 of mammalian cells. Erythropoiesis can be mo- 

 bilized much more rapidly in the fowl than m 

 the rabbit, as can be seen from the regeneration 

 curves for the two (Wright, 1930a, and 1930b), 

 even though on the basis of relative Ijlood vol- 

 umes the loss of blood is greater in the fowl. 

 Possibly the delay in the mammal is related to 

 the additional time necessary for the disposal of 

 the nucleus." 



Since immature stages are not hard to find 

 in circulating blood, it was thought that over-age 

 cells might also be easy to find. A few were 

 discovered but only after much searching. They 

 are not nearly so common as are the immature 

 stages. However, this statement is applicable 

 only to stages showing pyknosis and degenera- 

 tion; the early indications of aging are fairly 

 abimdant ( fig.' 25) . Within any one slide there 

 usually exists considerable varialnlity ni the nr- 

 tensity of nuclear staining. This variability is 

 illustrated in figure 2 and particularly in figure 

 3; the chromatin in some nuclei has the form of 

 fine particles and gives to the nuclei a light color, 

 but in others the chromatin is condensed and the 

 nuclei are darkly stained. It is these latter that 

 presumably are the older cells, and were they 

 not removed from the circulation Ijy the spleen, 

 they would go on to a pyknotic condition (fig. 

 26 ) . The pyknotic stages are rare. 



In pyknosis the first reactions consist of chro- 

 matin condensation and nuclear contraction, and 

 the spaces between the chromatin clumps are no 

 longer clear but take the same staining reaction 

 as the chromatin, although in a lighter shade. 

 On sectioned material it is hard to decide whether 

 this reaction is due to dissolution of basichroma- 

 tin into the nucleoplasm or to the filter effect of 

 underlying chromatin clumps that are out of 

 focus because the nucleus has greater thickness 

 than the oil inmierision lens has depth of focus. 

 The flattened nucleus of a cell in a blood smear, 

 however, lies within sharp-focus range of the 

 lens ; thus, the conclusion may be justified that 

 in the process of pyknosis some basichromatni 

 is dissolved in the nucleoplasm. This conclu- 

 sion is in agreement with observations made on 

 a previous study (Lucas, 1940) in which the 

 Feulgen test gave a positive reaction on the nu- 

 cleoplasm of degenerating tissue cells. 



As pyknosis proceeds in most tissue cells of 



the body, there is usually extensive contraction 

 of the nucleus that brings about considerable 

 change in the nucleocytoplasmic ratio. Some 

 evidence of this shift is shown in figure 26 but 

 a different type of reaction is equally common, 

 namely, vacuole formation within the nucleus 

 (figs. 27 and 28). This would appear to be a 

 compensatory reaction. The nucleus durmg 

 pyknosis should shrink but apparently the at- 

 tachment of nucleus to stroma will not permit an 

 overall retraction of the nuclear membrane. The 

 goblet-shaped vacuole in figure 28, with its stem 

 extending to the nuclear surface, suggests that 

 cytosomal fluids have been sucked in to form 

 these vacuoles, permitting increased condensa- 

 tion of the chromatin without loss of nuclear 



volume. 



Degenerating erythroc^-tes in the spleeii ex- 

 hibit predominantly nuclear contraction without 

 vacuolization; some show karyorrhexis. The 

 latter has never been observed in circulating 

 blood in mature erythocytes from normal birds. 



These degradation changes in the cell and its 

 nucleus are included under the section describing 

 normal circulating blood because aging and the 

 processes leading to death, as well as death itself, 

 are all normal phases of life's progression. But 

 whether degenerating cells normally occur in the 

 circulating blood of a healthy bird is another 

 question for which there is no answer at present. 

 A study on the occurrence of over-aged cells in 

 the circulating blood under various experimental 

 conditions should produce some interesting re- 

 sults. The bird lends itself to this type of study 

 Ijecause the nucleus is a more delicate indicator 

 than is the hemoglobin-bearing cytosome. In 

 mammalian blood there is no means for recogniz- 

 ing the old erythrocyte because the nucleus is 

 ejected or disintegrated before the cell enters the 

 circulation. 



Atypical and abnormal erythrocytes (figs. 

 30-49) 



Cells included in this group are those in which, 

 presumablv. the atvpical condition observed ex- 

 isted in the bird before the blood was drawn, 

 but there is alwavs the possibility that a particu- 

 lar result observed was produced by the technic 

 employed. 



Spindle cells (figs. 30-32) are rare in blood 

 from normal birds. It is conceivable that the 



30 



