THE BIOLOGY OF DAILY LIFE. 45 



in which float vast numbers of formed bodies, 

 the blood corpuscles. The great majority of 

 these are coloured : a few of them are colour- 

 less. The latter are called white or colourless 

 blood corpuscles, or leucocytes. The former are 

 called red or coloured blood corpuscles, or blood 

 discs. They appear red only when seen in a 

 thick layer ; when in a single layer they appear 

 of a yellow greenish colour, more yellow, if of 

 arterial, more green if of venous blood. 



" The proportions of plasma and blood 

 corpuscles are sixty-four of the former and 

 thirty-six of the latter in one hundred volumes 

 of blood. By measurement it has been found 

 that there are a little over five millions of 

 blood corpuscles in each cubic milimetre 

 (15625 of a cubic inch) of human blood. 

 There appears to be in healthy human blood 

 one white corpuscle for 600 1200 red ones. 

 In man and mammals the relative number of 

 blood corpuscles is greater than in birds, and 

 in birds greater than in lower vertebrates. 



"In a microscopic specimen of fresh unaltered 

 blood, the red blood corpuscles form peculiar 

 shorter or longer rolls, like so many coins, 

 from becoming adherent to one another by 

 their broad surfaces. Under various con- 

 ditions such as when isolated, or when blood 

 is diluted with saline solution, or solutions of 

 other salts (sulphate of sodium or magnesium) 

 tfie corpuscles lose their smooth circular outline, 

 shrinking and becoming crenate [i.e., notched 

 or indented]. In a further stage of this process 



