MORPHOLOGY OF THE BLOOD 125 



MORPHOLOGY OF THE BLOOD. 



The corpuscles floating in the fluid plasma of the blood, when separated 

 by a centrifugal machine are found to make up 45 to 50 per cent, of the total 

 mass of the blood. These corpuscles, or formed elements, are of three 

 varieties, the red corpuscles or erythrocytes, the white corpuscles leucocytes, 

 and the blood platelets which have been called thrombocytes. 



Red Corpuscles or Erythrocytes. Human red blood corpuscles are 

 circular, biconcave discs with rounded edges, from 7/4 to 8// in diameter, 

 and about 2 in thickness. When viewed singly they appear of a pale 

 yellowish tinge; the deep red color which they give to the blood being ob- 

 servable in them only when they are seen en masse. They are composed 

 of a colorless, structureless, and transparent filmy framework or stroma, 

 infiltrated in all parts by the red coloring matter, the hemoglobin. The 

 stroma is tough and elastic, so that as the corpuscles circulate they admit 

 of elongation and other changes of form in adaption to the vessels, yet 

 recover their natural shape as soon as they escape from compression. 



FIG. 109. FIG. no. 



FIG. 109. Red Corpuscles in Rouleaux. The rounded or uncolored corpuscles are 

 leucocytes. 



FIG. no. Corpuscles of the Frog. The central mass consists of nucleated colored 

 corpuscles. The other corpuscles are two varieties of the colorless forrn. 



Number and Character of the Red Corpuscles. The normal number of red 

 blood-cells in a cubic millimeter of human blood was estimated by Welcker, 

 in 1854, to be 5,000,000 in men and 4,500,000 in women. Numerous recent 

 observations, however, have shown that these estimates are a little low, 

 especially in men, and the average number has been placed by different 

 authorities at various points between 5,000,000 and 5,500,000. Still the 

 original numbers as given by Welcker are accepted at the present day as being 

 sufficiently accurate for ordinary purposes. It has been also shown that 

 there are many distinct physiological variations in the number, depending 



