SEC. 3. THE HISTORY OF THE CORPUSCLES. 



In the living body red blood-corpuscles are continually being 

 destroyed, and new ones as continually being produced. The proofs 

 of this are, 



/ 1. The number of the red corpuscles in the blood at any given 

 (time varies much. 



The number of corpuscles in a specimen of blood is determined by 

 mixing a small but carefully measured quantity of the blood with a large 

 quantity of some indifferent fluid, and then actually counting the 

 corpuscles in a known minimal bulk of the mixture. 



This may be done either by Yierordt's plan (somewhat modified by 

 Gowers), in which a minimal quantity of the diluted blood, measured 

 in a fine capillary tube, is spread on a surface marked out in square 

 areas, and the number of corpuscles in each square area counted under 

 the microscope; or by that of Malassez, in which the diluted blood 

 is drawn into a capillary tube with flattened sides, and the number 

 of corpuscles counted in situ in the tube by means of an ocular 

 marked out in squares, the microscope being so adjusted that each 

 area of the ocular corresponds to a certain capacity of the capillary tube. 



The average number of red corpuscles in mammals generally 

 ranges from 3 to 18 millions; in human blood it is about 5 millions 

 in a cubic millimetre. The number is increased by meals, and dimi- 

 nished by fasting ; of course, the number of corpuscles present in any 

 given bulk of blood being merely the expression of the proportion 

 of corpuscles to the amount of plasma, variations in the number 

 counted might and in certain cases are probably caused by an 

 increase or decrease in the quantity of plasma, occurring while the 

 actual number of corpuscles is stationary. But many of the 

 variations cannot be so accounted for ; they must be due to an in- 



