THE BLOOD CELLS 



71 



Erythrocytes. —These cells take their name from the red color 

 they give the blood en masse, but single cells have a pale yellow-green 

 color. In mammals the erythrocytes are enucleated, that is they 

 lose their nuclei before entering the circulating blood, but in other 

 vertebrates they are true cells, usually flattened ovals in shape, 

 with a central nucleus causing a cellular bulge. There is great 

 variation in their size in different species, as evidenced by the 

 following list of measurements: in Amphiuma (Fig. 40), which 

 has the largest, the cells are about 80 microns in diameter; in the 

 frog they are 22.3 by 15.7 microns; in the lizard they are 15.8 by 

 9.9 microns; in the rabbit the diameter is about 6.9 microns; in the 

 cat, (3.3 microns; in the musk deer, 2.5 microns; and in man, 7.5 



Fig. 40. — Photograph of blood cells of Amphiuma, showing erythrocytes and 



heterophils. 



microns. In many species, especially those with nucleated erythro- 

 cytes, there may be a considerable variation in size in the same 

 individual. 



When a drop of fresh mammalian blood is spread out in a thin 

 film on a glass slide, the erythrocytes tend to collect in groups 

 called rouleaux, strings of bi-concave discs. The formation of such 

 strings indicates a certain cohesiveness in the limiting membranes. 

 Two components of these cells ha\-e been distinguished, a stroma 

 or framework which is an optically homogeneous colloidal substance, 

 and hemoglobin which is a conjugated protein composed of globin 

 and a colored compoimd of iron called hemochromogen. The 



