over a wide range of developmental stages (Daw- 

 son, 1936a). 



A normal mature erythrocyte (fig. 24) has 

 been included in order to make the developmental 

 series complete. This forms the point of depar- 

 ture for the discussion of over-aged cells that 

 follows. In summary, it is quite evident that all 

 stages in erythropoiesis from the erythroblast to 

 the mature erythrocyte may be found in the cir- 

 culating blood. It would appear that birds in 

 general, including the chicken, have a more labile 

 hematopoietic system than mammals, and the 

 presence of an occasional immature red cell can- 

 not, at present, be regarded as abnormal or in- 

 dicative of a pathological or diseased condition 

 in birds. Wirth (1950) also obsei-ved greater 

 reactivity in chickens than in mammals and stated 

 that regeneration in the chicken was very vigor- 

 ous; that it ends in about a week, and that in mam- 

 mals a]:)out 3 weeks are necessary for the same 

 result. Polychromatic erythrocytes and ery- 

 throblasts occurred in very large numbers (up to 

 a half million per cubic millimeter) and the re- 

 ticulocytes became so numerous that they rose 

 from to 33 percent. 



Splenectomy in pigeons (Toiyii, 1930) raises 

 the number of polychromatic erythrocytes from 

 a control level of none to a quarter of a million 

 and more. This increase comes the first day 

 after splenectomy and continues for about 2 

 weeks and even after .50 days the level of im- 

 mature erythrocytes does not return to the nor- 

 mal. Jordan and Robeson (1942) observed 

 that splenectomy in pigeons increased the number 

 of plugged vessels and lymphoid foci in the bone 

 marrow. These authors interpret this as a com- 

 pensatory reaction but the possibility of a differ- 

 ent interpretation is discussed on page 181. 



Toryu (1931) also performed splenectomy on 

 pigeons and an abstract of his article (1933) 

 states: 



"After complete splenectomy the marrow of 

 the femur and tijjia becomes fatty and inactive 

 for erythrocyte formation, but active for lympho- 

 cyte formation; new haemopoietic tissue appears 

 m the lobules of the liver and various stages of 

 erythrocytes are seen in the central veins and the 

 capillaries of the acini. Splenectomy in adult 

 carrier pigeons brings about a general circula- 

 tion of polychromatophil cells, which amount to 

 3-8 percent of the red corpuscles in the blood. 

 The hemoglobin content after the operation does 



not reach the normal level, probably owing to the 

 presence of polychromatophils in the cir- 

 culation." 



Some physiological differences between ma- 

 ture and immature erythrocytes of birds, the 

 rate of maturation and the differences in these 

 respects between ijirds and mammals have been 

 brought out in studies made by Wright ( 1930a 

 and b) and Wright and VanAlstyne (1931), and 

 reviewed by Orten (1934). Wright made 

 use of the weU-established fact that immature 

 erythrocytes have a lower specific gravity than 

 mature erythrocytes. By centrifugation he sepa- 

 rated the reticulocytes and other more immature 

 erythrocytes from mature cells of chicken blood. 

 He obtained the immature cells by repeated 

 bleeding of adult birds and by injection of phen- 

 ylhydrazine hydrochloride. He estaljlished the 

 fact that the oxygen consumption of all types of 

 immature cells was greater than for mature cells. 

 This was true for mammals also, and it has 

 been suggested that perhaps most of the respira- 

 tion which occurs in mammalian erythrocytes is 

 due to the reticulocytes present. In summary, 

 Wright (1930b) says (p. 213): 



"A comparison is made of the respiration of 

 the reticulated nucleated red cells present in the 

 blood of anemic fowls and the nonnucleated retic- 

 ulated red cells of rabbits. On the basis of 

 equal volumes of cells, the respiration of the 

 former is about twice that of the latter, while 

 this in turn is aljout six times as great as the 

 nucleated but nonreticulated normal red cells 

 of the fowl." 



Wright and VanAlstyne (1931) has brought 

 out some significant points concerning the rate 

 of maturation of avian erythrocytes that may 

 help to account for the fact that recovery from 

 injury apparently is more rapid in ]>irds than 

 in mammals. They found in vitro that young 

 red cells could differentiate into mature erythro- 

 cytes within 36 hours, with a full complement of 

 hemoglobin. In fact, they state (p. 36) : 



". . . the conclusions are drawn that the baso- 

 philic staining characteristic of the more primi- 

 tive cells is no indication of any lack of hemo- 

 globin. Indeed the most primitive cells exam- 

 ined seem to have possessed almost, if not quite, 

 as much of this substance as the ordinary red 

 corpuscles." 



On the subject of rate of maturation they ob- 

 served (p. 32) : 



29 



