and more vacuoles. The nucleus is small in relation 

 to the cell area, and is darkly stained. There is a 

 clear area in the cytosome at the side of the nucleus. 



Mature plasmacyte.—The cell may vary in size from 

 large to small, and the cytosome contains numerous 

 granules, ranging from large to small. The nucleus 

 contains condensed blocks of chromatin and is located 

 against the cell wall. A clear area adjacent to the 

 nucleus is present in most mature plasmacytes. 



The definitions that have heen presented are 

 in reality brief descriptions of each cell type, 

 and the use of these, combined with the illustra- 

 tions, should make it possible to put together 

 quickly the necessary facts for identification of 

 any mature or immature cell without extensive 

 reading. 



Brief mention of some terms used in general 

 cytology may be helpful. The cell is composed 

 of two main parts — nucleus and cytosome; the 

 former contains nucleoplasm and the latter, cyto- 

 plasm. If a large dense mass of basichromatin 

 lies within the nucleus, it is called a karyosome 

 or karyosome nucleolus, and if the mass or sphere 

 takes acidophilic dyes, it is called a plasmosome 

 or plasmosome nucleolus, and if both karyosome 

 plasruosome are present, the two form an amphi- 

 nucleolus. 



Wherever color is mentioned, it is understood 

 that Wright's stain was used on smears of the cir- 

 culating blood of the hatched chicken, and May- 

 Griinwald Giemsa was used for immature cells 

 found in embryos and in hematopoietic organs of 

 both embryo and hatched chick. Any exceptions 

 to this have been noted in the legends or text. 

 These two stains give closely similar colors on 

 the same cell, but the latter produces a somewhat 

 more intense coloration. 



MAGNIFICATION 



The measureiuent of lilood cells is an im- 

 portant field of study, and especially so on eryth- 

 rocytes, which have a definite shape and are 

 held by a firm stroma. Some measurements of 

 length and of width of elongated cells and of 

 diameters of circular cells and of areas of ir- 

 regularly shaped cells have been undertaken in 

 this study. Not as much emphasis has been 

 put on cell size as in some atlases on human 

 blood. 



Size is a helpfid adjunct to cellular morphol- 

 ogy for the categorizing of cells into types and 

 into stages of development, but if one takes away 

 color, form, and internal structure, then size 

 alone becomes a rather inadequate tool for cell 

 identification. This is especially true of cells 

 prepared for study by the smear method, which 

 flattens them as broadly as their membranes will 

 permit. Smears from bone marrow and other 

 hematopoietic organs showed this quite clearly: 

 in an area where the smear was thick, the cells 

 were smaller, but at the edges of a group of cells 

 they were larger and, in many cases, were 

 stretched to the breaking point in drying. In the 

 wet-fixed smear the cells are luuch smaller than 

 in the dried smear and they often appear 

 shrunken. Compare, for example, the size of 

 basophils that have been fixed by drying in air 

 (fiijs. 385-387) with similar cells fixed in methyl 

 ak^ohol (figs. 388-390). 



Most often the visual impression of size as 

 seen microscopically forms the basis for the 

 statement that a cell is large, or medium, or small 

 and, only rarely, is the filar micrometer taken 

 out of the box and actual measurements of size 

 made. True, actual measurements should be 

 taken more often than they are, but the fact re- 

 mains that we depend to a great extent on mental 

 impressions for a comparative estimate of the size 

 of objects. Therefore, in order to avoid con- 

 fusion in making these impressions from the il- 

 lustrations, only two magnifications have been 

 ^igeJ — one called low power and the other, high 

 power. Two scales have been constructed (fig. 

 1, D and E). One, D, is equivalent to the 

 measurements in microns at a magnification of 

 1370 X and the other, E, at 2470 X- With these 

 scales the size of any cell or its part can be esti- 

 mated fairly closely, since all cells, both at low 

 and high magnification, were drawn carefully 

 with a camera lucida. 



The low-power drawings were made at an op- 

 tical magnification of 400 X and a magnification 

 when projected on drawing paper of 91 3.3 X. 

 The high-power drawings were made at an opti- 

 cal magnification of 1125X and a projected mag- 

 nification of 2470 X. By optical magnification 

 is meant the theoretical value obtained when the 

 magnification of the objective is multiplied by 

 the magnification of the eyepiece. The low- 

 power drawings were made by using a 20X ob- 

 jective and a 20X ocular, and the high-power 



14 



