126 



THE BLOOD 



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 



FIG. in. The Illustration is Somewhat Altered from a Drawing by Gulliver, in the 

 Proceed. Zool. Society, and exhibits the typical characters of the red blood-cells in the 

 main Divisions of the Vertebrata. The fractions are those of an inch, and represent the 

 average diameter. In the case of the oval cells, only the long diameter is here given. It is 

 remarkable, that although the size of the red blood-cells varies so much in the different 

 classes of the vertebrate kingdom, that of the white corpuscles remains comparatively 

 uniform, and thus they are, in some animals, much greater, in others much less, than the 

 red corpuscles existing side by side with them. 



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 



