THE BLOOD. 



77 



After a short delay, the red corpuscles which have sunk to the bottom 

 of the cell, and are resting on the squares, are counted in ten squares, 

 and the number of white corpuscles noted. By adding together the 

 numbers counted in ten (one-tenth millimetre) squares, and multiplying 



FIG. 76. Heemacytometer. 



by ten thousand, the number of corpuscles in one cubic millimetre of 

 blood is obtained. The average number of corpuscles per each cubic 

 millimetre of healthy blood, according to Vierordt and Welcker, is 

 5,000,000 in adult men, and rather fewer in women. 



CHEMICAL COMPOSITION OF THE BLOOD. 



Before considering the chemical composition of the blood as a whole, 

 it will be convenient to take in order the composition of the various 

 chief factors which have been set out in the table on p. 58, into which 

 the blood may be separated, viz. : (1.) The Plasma ; (2.) The Serum; 

 (3.) The Corpuscles ; (4.) The Fibrin. 



(1.) Chemical Composition of Plasma. The Plasma, or liquid 

 part of the blood, in which the corpuscles float, may be obtained free 

 from colored corpuscles in either of the ways mentioned below. 



In it are the fibrin factors, inasmuch as when exposed to the ordinary 

 temperature of the air it undergoes coagulation and splits up into fibrin 

 and serum. It differs from the serum in containing fibrinogen, but in 

 appearance and in reaction it closely resembles that fluid; its alkalinity, 

 however, is less than that of the serum obtained from it. It may be 

 freed from white corpuscles by filtration at a temperature below 41 F. 

 (5 C.), or by the centrifugal machine. 



