Avian blood serum contains more particles 

 than mammalian serum. Usually the serum 

 does not give trouble in stained smears from 

 young birds or males, but it may be quite annoy- 

 ing in laying birds, in circulating blood from em- 

 I)ryos, in bone marrow of older birds, and espe- 

 cially in bone marrow of embryos (fig. 322). 

 The granules in the serum (figs. 69 and 72) tend 

 to stain more readily with Wright's than with 

 May-Griinwald Giemsa. Wlienever they stain 

 they spread a veil or screen over the cells (fig. 

 72 ) and obviously make it difficult to observe 

 cellular detail. In addition, they modify the 

 color reaction of the underlying cells so that iden- 

 tification of cells under these conditions becomes 

 unreliable. In some cases only the granules take 

 the stain and in other cases both the fluid serum 

 and its contained granules take the basophilic 

 dye. Extreme examples are shown in embryo 

 ])one marrow (fig. 322), spleen (fig. 329), and 

 thymus (fig. 332). 



Sometimes the granules that fall on top of the 

 cell and not between the cells will take the dye, 

 which causes the cell to look as if it contains many 

 small organisms. Oftentimes the serum granules 

 will remain uncolored except near a ruptured or 

 smudged cell (figs. 175 and 176). In these fig- 

 ures the small, darkly stained particles are the 

 serum granules. Heterophil granules from the 

 rods may closely resemble those in the serum but 

 are larger and take a more reddish color. 



Occasionally the serum bodies are larger than 

 usual, resemble cocci, and may cluster around 

 the cells (fig. 69). This example was from a 

 heated slide but similar reactions have been seen 

 in unhealed specimens. 



Another type of abnormality obsei^ved both in 

 mammalian and in avian blood is the production 

 of slender, flexilsle, protoplasmic processes from 

 the surface of erythrocytes. They are not found 

 in fixed and dried smears but the projections on 

 cells A and B of figure 29 indicate their appear- 

 ance, except that they are longer in the living cell 

 where they are usually seen. Shipley (1916) 

 observed them in tissue culture from cells of the 

 area opaca, and found that they appeared to be 

 beaded for part or all of their length and termi- 

 nated in a small round knob. They were ac- 

 tively motile and the end of the process whipped 

 back and forth. 



Knowles et al. (1929) have depicted in color 

 many artifacts, abnormal cells, and cellular para- 



sites that are frequently found and misinter- 

 preted. Their studies covered several classes 

 of vertebrates, including birds. Some addi- 

 tional artifacts and parasites found in avian 

 blood are shown in the colored illustrations by 

 Balfour (1911). Neave (1906) pictured, in 

 figures b and c of plate XXI, two pointed objects 

 found in his blood smears. Similar objects have 

 been found on rare occasions in smears made 

 from the blood of chick embryos. Neave de- 

 scribes these bodies as follows (pp. 196-197): 

 ". . . Length varies from 50-58m and it occurs 

 plentifully. It would appear to consist of a 

 sheath jDointed at each end which contains proto- 

 plasm segmented into two or more portions." 

 Balfour (1911) considers these to be yeast cells 

 that have fallen on the slide and which have come 

 from the air. We are in agreement that they 

 are contaminants on the slide from outside the 

 specimen itself. 



THROMBOCYTES 



The nucleated thrombocytes of birds, reptiles, 

 amphibians and fishes have the same function as 

 the blood platelet in mammals. 



Bradley (1937) called these cells thigmocytes. 

 "Spindle cells" is anotlier term used commonly, 

 especially in the older literature. When blood 

 is drawn, tlirombocytes and platelets clump rap- 

 idly and soon disintegrate. The disintegration 

 is part of the mechanism of blood coagulation. 

 In mammals platelets are pinched off from the 

 cytosome of megakaryocytes located in the bone 

 marrow and lungs. The parent cell is large, 

 and is easily recognized and identified. It has 

 a polymorphonucleus in contrast to the multinu- 

 cleated condition of giant cells in birds. The 

 megakaryocyte is lacking in avian bone marrow 

 and, instead, thrombocytes arise from antecedent 

 mononucleated cells that have a blast stage like 

 that of other blood cells. Blount (1939b) noted 

 that thrombocytes of 5 x lOyu were smaller than 

 erythrocytes of 7 x 12^, and Magath and Hig- 

 gins ( 1934) gave the average size at 3.9 x 8.1 m- 

 The distribution curves for width and length, 

 based on 10 cells measured from each of 9 chick- 

 ens, gave means of 4.7 and 8.5 for tliese two 

 dimensions (fig. 89). These data are discussed 

 further in chapter 6. Similar distribution 



41 



