iv THE BLOOD : FOKMED CONSTITUENTS 105 



ascertain the variations due to age, sex, constitution, functional 

 state of the body, various morbid conditions of the blood, and so 

 on. As an average it may be taken that 1 c.mm. contains 5,000,000 

 red corpuscles in a man, 4,500,000 in a woman ; that they are 

 more abundant in venous than in arterial blood ; less abundant 

 in adolescents than in adults, more numerous in new-born infants 

 than in the mother; that all the influences that induce a marked 

 loss of water in the body increase their number, while a high 

 intake of water diminishes them ; that they multiply with every 

 improvement in the external and internal conditions of life, while 

 poor food and a vast number of morbid conditions tend to reduce 

 them. 



It is remarkable that the lowering of atmospheric pressure 

 on high mountains produces a considerable increase in the number 

 of erythrocytes (Viault). The same effect has been observed in 

 mice on rubbing their skin with croton oil, and on prolonged 

 exposure to strong electric light (Kronecker). It should also be 

 noted that not merely scanty nutrition, but even an absolute fast 

 of thirty days, produces no marked variation in the number of 

 the erythrocytes (Luciani). Obviously the relative quantity of 

 corpuscles, which depends upon the degree of concentration and 

 amount of water contained in the blood, can rarely yield a safe 

 conclusion as to the absolute quantity to be found in the total 

 mass of blood. 



The volume and surface of the erythrocytes have been 

 approximately determined, by using models of enormous magnifica- 

 tion ; 5,000,000 corpuscles are found to have a volume of about 

 % c.nim. and a surface of 610 sq. mm. 



The specific gravity of erythrocytes is, as- already stated, 

 greater than that of plasma and serum (1*088-1*105). The weight of 

 the corpuscles contained in 100 grnis. of defibrinated blood is not 

 far short of that of the serum, averaging a weight of 48 grms. in 

 man and 35 grms. in woman. Given a man of 78 kilograms, 

 whose blood amounts to ^ of his body- weight, the total weight 

 of the erythrocytes would be about 2 kgrin., with a total surface 

 of some 3840 sq. metres. 



VII. The pigment which colours the erythrocytes is a 

 compound of highly complex chemical structure, known as 

 Haemoglobin. Under physiological conditions it is entirely absent 

 from the plasma, and exclusively saturates the colourless spongy 

 mass of the corpuscle, termed by Eollet the sfroma. This fact 

 suggests that it may be in chemical combination with one of the 

 constituents of the stroma, perhaps with the lecithin (Hoppe- 

 Seyler). But the most certain and most important property of 

 the pigment, and that on which the capital function of the 

 erythrocytes depends, is its affinity for oxygen, with which it 

 combines as soon as the partial pressure of the gas reaches a 



