THE BLOOD 239 



the corpuscle presents in its peripheral portion a bright rim, and in its cen- 

 tral portion a dark spot If the objective be brought nearer and the center 

 accurately focused, the reverse appearance obtains; the central portion 

 becomes bright and the peripheral portion dark. The cause of this differ- 

 ence in optical appearance is the unequal distribution of the transmitted 

 light in consequence of the shape of the 

 corpuscle. 



Size. The diameter of a typical well- 

 developed red corpuscle under normal con- 

 ditions is 0.0075 mm., its greatest thick- 

 ness is 0.0019 mm. Though this may be FIG. 92. IDEAL TRANSVERSE 

 assumed as the average diameter, there SECTION OF A HUMAN RED CORPUS- 



,. . , CLE. (Magnified 5000 times.) a. b. 



is a small percentage of distinctly smaller Diameter, c, d. Thickness. 

 and a small percentage of distinctly larger 



corpuscles. The following table shows the results of measurements made 

 by different observers: 



Normal Limits. Average Diameter. 



Welcker diameter 0.0045-0.0095 mm 0.0070 mm. 



Hayem diameter o .0060-0 .0088 mm o .0075 mm. 



Gram diameter 0.0067-0.0093 mm 0.0078 mm. 



Melassez 0.0076 mm. 



0.00747 (33^ inch) 



Structure. The red corpuscle of man as well as of all other mammals 

 possesses neither a nucleus nor a limiting membrane, but appears to consist 

 of a homogeneous substance more or less semisolid in consistence. 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 retractility. 



The foregoing is the classic and generally accepted view as to the shape, 

 size, and structure of the red corpuscle. Nevertheless recent investigations 

 render it probable that the statements were based on observations of the 

 corpuscles under artificial rather than natural conditions, and therefore not 

 strictly true. For many years histologists from time to time have stated 

 that the red corpuscle is not circular and biconcave in shape, in the cir- 

 culating blood, but bell-shaped, similar to that shown in Fig. '95. It was 

 not until 1902, after the publication of Weidenreich's investigations, that 

 this view began to receive more attention than had hitherto been accorded 

 it. Weidenreich preserved in a moist chamber a hanging drop of human 

 blood, and on examination found that the red corpuscles were bell-shaped 

 though the depth of the bell cavity varied considerably. An examination 

 of the capillary circulation in the omentum of the rabbit revealed the fact 

 that the corpuscles in their natural medium were also bell-shaped. The 

 circular biconcave shape they ordinarily present when a drop of blood is 

 examined microscopically he attributes to cooling, evaporation and con- 

 centration of the drawn blood. Experimentally it was shown that when 

 blood was added to 0.6 to 0.65 per cent, solution of sodium chlorid all the 

 corpuscles were bell-shaped, but if the solution was increased or decreased 

 in strength, this form was at once changed. 



