THE BLOOD. 2 37 



together, the color deepens and the corpuscles appear red. In either 

 case the color is due to the presence in the corpuscle of a specific 

 coloring-matter, hemoglobin. 



Shape. The red corpuscle is a circular ? flattened disk with 

 roundededges. Each surface is perfectly s~moofK""ancFpresents a 

 sHallow depression in its center, so that it is also biconcave. A 

 longitudinal section of a corpuscle would present, when viewed 

 edgewise, an outline similar to that of Fig. 97. This difference in 

 the thickness of the peripheral and central portions of the corpuscle 

 gives rise to differences in optical 

 appearances when examined micro- 

 scopically. At a certain distance of 

 the object-glass the corpuscle pre- 

 sents in its peripheral portion a 



bright rim, and in its central por- FlG - 97- IDEAL TRANSVERSE SEC- 

 , ,' Tr , ,. F . TION OF A HUMAN RED CORPUS- 



tion a dark spot. If the objective CLE . (Magnified 5000 times.) 



be brought nearer and the center a, b. Diameter, c, d. Thickness, 



accurately focused, the reverse ap- 

 pearance obtains; the central portion becomes bright and the periph- 

 eral portion dark. The cause of this difference in optical appear- 

 ance is the unequal distribution of the transmitted light in conse- 

 quence of the shape of the corpuscle. 



Size. The diameter of a typical well-developed red corpuscle 

 under normal conditions is o.cx>25_ mm. ; its greatest thickness is 

 0.0019 mm. Though this mayT)e assumed as the average diameter, 7 '\ 

 there is a small percentage of distinctly smaller and a small per- 

 centage of distinctly largdf corpuscles. The following table shows 

 the results of measurement made by different observers : 



Normal Limits. Average Diameter. 



Welcker, diameter 0.0045-0.0095 0.0070 



'Hayem, " 0.0060-0.0088 0.0075 



Gram, " 0.0067-0.0093 0.0078 



Melassez, " ____ 0.0076 



0.00747 

 (Woo inch ) 



Structure. The red corpuscle of man as well as all other mam- 

 mals possesses neither a nucleus nor a limiting membrane, but appears 

 to consist of a homogeneous substance more or less semisolid in con- 

 sistence. Under the influence of certain reagents the corpuscle 

 separates into two distinct portions: viz., a colorless protoplasmic 

 stroma and a coloring-matter which diffuses into the surrounding 

 liquid. The presence of the former can be demonstrated by the 

 addition of iodin, which imparts to it a faint yellow color. The 

 stroma is elastic, and determines not only the shape of the corpuscle 

 but gives to it the properties of extensibility and retractibility. 



