262 



THE HUMAN BODY 



after blood is drawn the 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 



FIG. 98. 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 

 C one is seen edgewise. F, G, H, I, white corpuscles highly magnified. 



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. 



Structure. There is no satisfactory evidence that these cor- 

 puscles have any enveloping sac or cell-wall. All the methods 

 used to bring one into view under the microscope are such as 

 would coagulate the outer layers of the substance composing the 

 corpuscle and so make an artificial envelope. So far as optical 

 analysis goes, then, each corpuscle is homogeneous throughout. 

 By other means we can, however, show that at least two materials 

 enter into the structure of each red corpuscle. If the blood be 

 diluted with several times its own bulk of water and examined 

 with the microscope, it will be found that the formerly red cor- 

 puscles are now colorless and the plasma colored. The dilution 

 has caused the coloring matter to pass out of the corpuscles and 

 dissolve in the liquid. This coloring constituent of the corpuscle is 



