70 BLOOD 



rial structure, and in their mature form possess no semblance of a 

 nucleus. Nucleated red blood cells in man are only found as pre- 

 mature forms in the hemopoietic tissues and in the circulating 

 blood in early embryonic life. In the later periods of fetal life, 

 and even in the first year of childhood, an occasional nucleated 

 red cell may be demonstrated in the blood current. Diseased con- 

 ditions, involving rapid regeneration of blood cells, are, however, 

 frequently accompanied by the appearance within the general 

 blood current of nucleated red cells, erythroblasts, in considerable 

 numbers. 



Effect of Reagents upon the Red Blood Cells. The effect of 

 certain reagents upon the red cells throws much light upon their 

 finer structure, and especially upon their relation to osmotic proc- 

 esses. The red cells apparently exist within the blood, floating 

 free in its plasma, in a state of osmotic stability ; the plasma is 

 then an isotonic solution as regards the red cell. Should the spe- 

 cific gravity of the blood plasma be in any way increased, it imme- 

 diately becomes hyperisotonic for the red cell ; should, on the other 

 hand, the specific gravity be diminished, the plasma becomes hyp- 

 isotonic. It should be borne in mind that osmotic flow occurs in 

 a direction from the lighter toward the heavier fluid. 



Water. The addition of water to the blood plasma diminishes 

 the specific gravity of the latter, and produces an osmotic flow into 



the red cells. The corpuscles promptiv 

 a I c d e ,, , ,, . , . 5 



8ft & fb r*} swell, lose their biconcave shape, and 

 fj gp \ir v_y finally, from the extreme distention, 

 Fio. 75. SHOWING THE ACTION their limiting membranes apparently 

 or WATER UPON THE RED rupture ^ permit the escape of the 



BLOOD CELL. , ' . 



a, the cell in profile; 6-,, hemoglobin; the remaining colorless 

 various stages in the transfer- stroma of the red cells forms the so- 

 mation which leaves only a ca n e d " blood-shadows." The rapidity 



"shadow" e\ diagrammatic. , , , , . ,. , , 



(After Schafer.) * these changes is apparently dependent 



upon the amount of water added to the 



plasma, and therefore upon the degree of hypisotonicity produced 

 in the latter. 



Saline Solutions (hyperisotonic). Solutions of sodium chlorid, 

 magnesium sulfate, etc., whose specific gravity is greater than 

 that of the blood plasma, when added to the blood produce a con- 

 dition of hyperisotonicity. The consequent osmosis takes place 

 from the corpuscle to the plasma ; the corpuscular wall promptly 

 collapses and presents an irregular spinous or serrated profile 



