BLOOD 193 



variations in their haemoglobin content and in, the surrounding plasma. 

 Occasionally they are spherical (according to Schultze, and others), and 

 deviations from the primary cup-shaped form are to be expected. In 

 these changes the corpuscles act like membranes filled with fluid. In 

 the mature corpuscles, however, the outer layer is thick, blending with 

 the contents within; and since no sharp bounding line can be seen histo- 

 logically, the corpuscles have been described as lacking membranes. 

 The plastic nature of the membrane is shown by heating the blood film. 

 The corpuscles then become globular and send out slender varicose 

 processes, or round knobs attached by pedicles (Fig. 184, H). These 

 small spheres become detached in great numbers. 



The dimensions of red corpuscles are quite constant. Those in human 

 blood average 7.5 n in diameter and ordinarily vary from 7.2 to 7.8 /*. 

 They sometimes surpass these limits. In biconcave form they are about 

 1.6 n thick. The cups average 7 ju in diameter and are 4 n in depth. 



FIG. 184. RED CORPUSCLES IN VARIOUS CONDITIONS. 



Spherical corpuscles are said to be 5 n in diameter. The blood of mammals 

 other than man also contains cups which become discs. The latter are 

 oval in the camel group but round in all others. Their average diameters 

 are less than in man (7.3 ju in the dog, 7.48 n in the guinea-pig), but the 

 species of animal cannot satisfactorily be determined from the diameter 

 of the corpuscles. In a given section, as already noted, the red corpuscles 

 furnish a useful gauge for estimating the size of other structures. 



The number of red corpuscles in a cubic millimeter of human blood 

 averages five million for men, and four million five hundred thousand for 

 women. By diluting a small measured quantity of blood and spreading 

 it over a specially ruled slide, the corpuscles may be counted, and the 

 number per cubic millimeter calculated. A diminished number is of 

 clinical importance. 



Histologically the red corpuscles usually appear as homogeneous 

 bodies, but with special methods a granular network has been found 

 within them, which has been interpreted as a reaction of the haemoglobin 

 to reagents, and also as a persistence of the protoplasmic reticulum of 

 the erythroblasts. It occurs especially in newly formed corpuscles 

 (seen in cases of anaemia). Instead of a net, there may be rings or round 

 13 



