THE BLOOD AND THE LYMPH 265 



dry under the microscope. Weidenreich (following Leeuwenhoek of 

 two hundred years ago) has recently claimed that the erythrocytes are 

 normally cup-shaped or even spherical, collapsing quickly when shed. 

 This shape may be readily seen when the corpuscles are drawn from 

 the animal into an excess of Senkler's fluid. It is more likely that this 

 shape is a distortion caused by the powerful reagents in a manner not 

 unlike the action of heat already noted. One of the unexplained peculiar- 

 ities of the red corpuscles is their strong tendency when shed to collect 

 in rouleaux like rolls of coin, as if the rims of these minute biconcave 

 disks had some sort of attraction for each other. 



The size of the human erythrocyte is of considerable medico-legal 

 importance. On the average a red corpuscle is about seven and seven- 

 tenths micromillimeters (7.7 microns) in diameter (a micromillimeter 

 or micron being the thousandth part of a millimeter), and one-quarter 



FIG. 138 



Erythrocytes as seen under certain conditions. This appearance is the basis of the recent 

 claims that the normal functioning corpuscles are spherical. 



as thick. The normal variation in diameter ranges between about 6.5 

 and 9.5 microns. When the blood is more watery than usual the 

 corpuscles swell, while fever and inanition are said to occasion their 

 shrinkage. (Further important details of much diagnostic importance, 

 concerning the number, size, and shapes of the red corpuscles, are to be 

 had from text-books on hematology.) 



The number of the erythrocytes varies in many different conditions of 

 health as well as of disease, but there is for each sex an important normal 

 average from which as a standard clinical blood-counts are made. 

 Males have about five million erythrocytes to every cubic millimeter 

 of their blood and adult females about four-and-a-half millions of them. 

 Thus every cubic centimeter of a man's blood contains five thousand 

 million erythrocytes. 



The places of origin of the red corpuscles in the fetus seem to be in the 



