THE BLOOD. 



243 



situation both arterial and venous capillaries are relatively large and the 

 blood is separated from the surrounding marrow by extremely thin walls. 

 In the passages of this capillary network the erythroblasts make their appear- 

 ance most probably by a transformation of pre-existing marrow cells. At 

 first they are large, homogeneous, colorless, perhaps slightly tinged with 

 hemoglobin and distinctly nucleated. They increase in number by kary- 

 okinesis and at the same time increase in their hemoglobin content. In the 

 course of their development the nucleus becomes smaller and denser, when 

 the cells are known as normoblasts. Subsequently the nucleus is extruded, 

 carrying with it a portion of the perinuclear cytoplasm, after which the 

 remainder of the corpuscle assumes the shape and size of the adult corpuscle 

 and is carried out into the general circulation. After severe hemorrhage 

 the formative processes in the marrow may become so active that erythro- 

 blasts and normoblasts make their appearance in the blood-stream before 

 the extrusion of the nucleus has taken place. 



CHEMIC COMPOSITION OF RED CORPUSCLES. 



When analyzed chemically the red corpuscles are found to consist of 

 water 65 per cent, and solid matter 35 per cent. The solids, moreover, have 

 been found to consist of a pigment hemo- 

 globin 33, protein 0.9, cholesterin and 

 lecithin 0.46, and inorganic salts (chiefly 

 potassium phosphate and chlorid and 

 sodium chlorid) 1.4 per cent, respectively. 

 Of the total solids the hemoglobin con- 

 stitutes about 94 per cent. 



Hemoglobin. In the normal condi- 

 tion of the corpuscle the hemoglobin is in 

 an amorphous condition and is com- 

 bined in some unknown way with the 

 stroma. 



When hemoglobin is decomposed in 

 the absence of oxygen it undergoes a 

 cleavage into a protein, globin, and an 

 iron-holding pigment hemochromogen 

 which constitutes about 4 per cent, of 

 the molecule. If a solution of hemo- 

 chromogen be exposed to air it absorbs 

 oxygen and is converted into hematin. 

 This latter compound can also be de- 

 rived directly from hemoglobin by the 

 action of acids and alkalies. It is to the 

 presence of hemochromogen in combina- 

 tion with the protein globin that the 

 hemoglobin is indebted for its power of 

 absorbing and carrying oxygen. 



If blood which has been rendered laky, by water or any other of the 

 known agencies, be allowed to evaporate slowly, the dissolved hemoglobin 



FIG. 105. CRYSTALLIZED H E M o 

 GLOBIN. a, b. Crystals from venous 

 blood of man. c. From blood of cat. 

 d. Of guinea-pig, e. Of. marmot. /. 

 Of squirrel. (Gautier}. 



