108 THE BLOOD 



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 adaptation to the vessels, yet 

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



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 





FIG. 109. FIG. no. 



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

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

 The other corpuscles are two varieties of the colorless form. 



on the time of day, digestion, sex, etc. The number of red cells usually 

 diminishes in the course of each day, while the leucocytes increase in number. 

 It has been suggested that this is due to the influence of digestion and exercise. 

 It has generally been found that within half an hour or an hour after a 

 full meal the number of red cells begins to diminish, and that this keeps up 

 for from two to four hours, when it is followed by a gradual rise to the normal. 

 The usual fall is 250,000 to 750,000 per cubic millimeter. These results 

 are most marked after a largely fluid meal, and are probably due to dilution 

 of the blood as a result of the absorption of fluids. In animals the number 

 of red cells is increased by fasting, but in man the results are variable, some 

 authorities claiming an increase and others a decrease. In childhood there 



