684 



HUMAN ANATOMY. 



Fig. 648. 



when subjected to saline solutions stronger tlian the "normal," the exterior of the corpuscles 

 becomes irregular and beset with knob-like projections or spines. When the concentration 

 of the medium is increased, the "crenation" gives place to marked shrinkage and distortion, 

 until the cells lose all resemblance to their normal form. 



Upon treatment with water, aqueous dilutions of acetic acid, ether, and other reagents, the 

 erythrocytes are promptly decolorized by the extraction of the hemoglobin. An interesting 

 modification of the phenomenon may be produced by solutions of tannic acid or potassium 

 bichromate of varying strength. When the reaction is vigorous, the decomposed hemoglobin 

 is caught within the cell and appears as a mass somewhat resembling a nucleus. When the 

 reaction is feeble, as with very weak solutions, the hemoglobin is less suddenly precipitated, and 

 appears as a minute projection attached to one part of the exterior of the decolorized corpuscle. 

 Alkaline solutions effect the complete destruction of the red cells. Among the reagents 

 employed in histological investigations, osmic acid (i per cent.) deserves especial confidence as 

 preserving the form of the red corpuscles. Fixation by heat, so commonly used in the prepara- 

 tion of blood specimens for clinical examinations, produces alterations and often marked changes 

 in the red cells, and, therefore, is unsuitable for histological study of these elements. Attenua- 

 tion of the central parts of the cells produces appearances that have been mistaken for a nucle- 

 ated condition of the erythrocytes. Upon cautious application of heat, with precautions against 

 evaporation and drying, the corpuscles extrude portions of their substance which, after separation, 

 resemble miniature red cells. 



The Colorless Blood-cells. — It may 

 at once be emphasized that the colorless cells 

 observed within the blood are only incident- 

 ally related to the red cells and, further, that 

 they, in part at least, primarily circulate within 

 the lymph- vascular system, from which they 

 are poured into the blood. 



When examined in fresh and unstained 

 preparations, the colorless cells or leuco- 

 cytes appear as pale nucleated elements 

 which, by their pearly tint and refracting 

 properties, are readily distinguished from the 

 much more nuinerous surrounding erythro- 

 cytes. Their shape is very 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 these cells 

 soon exhibit amoeboid motion, whereby are 

 produced not only alterations in their form, but often also changes in their actual 

 position. 



A nucleus is always present, but may be obscured in the contracted spherical 

 condition of the cell by the overlying granular cytoplasm. In the expanded con- 

 dition, as when the cell is undergoing amoeboid change, the nucleus is very evi- 

 dent and the cytoplasm often differentiated into a homogeneous peripheral zone 

 {exoplasm^ and a central granular area (cndop/asm) surrounding the nucleus. A 

 distinct cell-wall is absent, although it is probable that a slight peripheral condensa- 

 tion serves to outline the corpuscle. That such condensation does not constitute a 

 definite envelope is shown by the readiness with which foreign particles may be taken 

 into the body of the cell. 



Although the size of the colorless corpuscles varies with the type of the cell, as 

 presently described, in general the diameter of these elements is larger than that of 

 the erythrocytes, and is commonly from .010-012 mm. Their number is much less 

 than that of the red corpuscles, the usual ratio between the white and red cells being 

 about 1 : 600. Even within physiological limits this ratio varies considerably, from 

 5000 to 10,000, with an average of 7500, white cells being normally found in one 

 cubic millimeter of blood. 



blood-cells seen in 

 small lymphocytes ; 



Varieties of coloriess 

 normal human blood ; o, 



b, large lymphocyte or mononuclear leucocyte; 



c, transitional leucocyte ; rf, polymorphonuclear 

 leucocytes; e, eosinophile ; /, red cells. X 900. 



Critical examination of the colorless cells, after fixation and staining, has shown that among 

 the elements collectively designated as the "white cells" or "leucocytes," five varieties are 

 usually present in normal blood. Since the recognition of these forms is sometimes of practical 



