THE INTERNAL MEDIUM. 



45 



outline according as it is looked at from the front or edge- 

 wise or in three-quarter profile. 



Sometimes the corpuscle (Fig. 13, B] appears circular; 

 then it is seen in full face; sometimes linear ((?), and slightly 

 narrowed in the middle; sometimes oval, as the dollar when 

 half-way between a full and a side view. These appearances 

 show that each red corpuscle is a circular disk, slightly hol- 

 lowed in the middle (or biconcave) and about four times as 

 wide as it is thick. The average transverse diameter is 0.008 

 milimeter (^Vo inch). Shortly after blood is drawn the 



FIG. 13. Blood-corpuscles. A, magnified about 400 diameters. The red corpus- 

 cles have arranged themselves in rouleaux ; a, a, colorless corpuscles ; B, red cor- 

 puscles more magnified and seen in focus : E. a red corpuscle slightly out of focus. 

 Near the right-hand top corner is a red corpuscle seen in three-quarter face, and at 

 Cone seen edgewise.' F, (?, H, I, white corpuscles highly magnified. 



corpuscles arrange themselves in rows, or rouleaux, adhering 

 to one another by their broader surfaces. 



Color. Seen singly each red corpuscle is of a pale yellow 

 color; it is only when collected in masses that they appear 

 red. The blood owes its red color to the great numbers of 

 these bodies in it; if it is spread out in a very thin layer it, 

 too, is yellow. In a cubic millimeter (^ inch) of blood there 

 are about five million red corpuscles. 



Structure. Seen from the front the central part of 

 each red corpuscle in a certain focus of the microscope 

 appears dimmer or darker than the rest (Fig. 13, B), ex- 



