NORMAL HISTOLOGY. 



and beset with knob-like projections, or crenated; increased concentration of 

 the solution leads to marked shrinkage and distortion, until the cells lose all 

 resemblance to their usual form. Certain reagents, as water, aqueous dilutions 

 of acetic acid and ether, promptly decolorize the erythrocytes by extraction 

 of the hemoglobin. Alkaline solutions completely destroy the red cells. 



The Colorless Blood-Cells. The colorless cells observed within the 

 blood are probably only incidentally, not genetically, related to the erythro- 

 cytes; further, they, in part at least, primarily circulate within the lymph- 

 vascular system, from which they are poured into the blood. They are not 

 confined, however, to the blood- and lymph-vessels, but occur also in bone- 

 marrow, lymphoid tissue and, as the "wandering cells," within the connec- 

 tive and epithelial tissues. Their distribution, therefore, is a very wide one. 

 When examined in fresh and unstained preparations, the colorless cells 

 or leucocytes appear as pale nucleated elements which, by their pearly tint 

 and refracting property, are readily distinguished from the much more 



numerous erythrocytes. Their shape 

 is variable, but when first withdrawn 

 from the body is usually irregularly 

 spherical or oval. When placed on 

 a warmed slide and maintained at 

 the temperature of the body, many 

 of the colorless cells exhibit amoeboid 

 motion, whereby not only alterations 

 in their outlines but also changes in 

 their actual position are produced. 

 Although always present, the nucle- 

 us may be obscured by the overlying 

 cytoplasm; it is most distinct when 

 the cell is expanded, as when under- 

 going amoeboid changes. A distinct 

 cell-wall is absent, although probably 

 the most superficial zone of cyto- 

 plasm possesses slightly greater den- 

 sity. The size of the colorless corpuscles varies with the type of the cell, as 

 described below, but in general their diameter is larger than that of the 

 erythrocytes, being commonly from 10-12 //. Their number is much less 

 than that of the red cells, the usual ratio being about one colorless to six 

 hundred red cells. Even within physiological limits this ratio varies con- 

 siderably, from 5000 to 10,000, with an average of 7500, white cells being 

 normally found in one cubic millimeter of human blood. 



After fixation and staining (see frontispiece), five varieties of colorless 

 cells may usually be distinguished in normal blood. 1 Two of these 



FIG. 133. Varieties of colorless blood-cells seen in 

 normal human blood ; a. small lymphocytes ; b, large 

 lymphocyte or mononuclear leucocyte ; c, trans- 

 itional leucocyte ; rf. polymorphonuclear leucocytes ; 

 f, eosinophile ; /, red cells. X 900. 



are 



1 It should be noted that the differentiation of these cells is founded upon not 

 only their morphological characters, but also the behavior of the granules embedded 

 within their cytoplasm when subjected to certain combination stains. A generation 

 ago Ehrlich divided the aniline dyes into three groups acid, basic, and neutral. The 

 first includes such dyes as acid fuchsin, orange G or eosin, in which the coloring prin- 

 ciple acts or exists as an acid and exhibits an especial affinity for the cytoplasm. 

 The second group, the basic stains, includes dyes, as hematoxylin. methylene-blue, 

 methyl-violet, methyl-green or thionin, in which the coloring principle exists chemi- 

 cally as a base in combination with a colorless acid and particularly affects the chro- 

 matin; hence such are nuclear stains. Neutral dyes, produced by mixture of 

 solutions of an acid and a basic stain, have a selective affinity for certain so-called 

 neutrophilic granules. 



