178 THE BLOOD 



Mill, per c.mm. 



Goat 14-19 



Lama . 13-13.2 



Sheep 10.3 



Cat 9.1 



Horse 7.8 



Monkeys 6.2 



Rabbit. 6.8 



Dog 6.7 



Birds 2.3 



Fish (bony) ' 1.2 



Reptilia 0.5-1.6 



Amphibia : frog 0.5 



Salamander . 09 



The average number of red corpuscles in one cubic millimeter of 

 human blood is given as 5,000,000; in woman, however, tneir number 

 is somewhat smaller, namely, about 4,500,000. In infants a higher 

 count is usually obtained than in adults. During the first weeks it 

 averages about 5,580,000, during the first and second years 5,680,000, 

 and from the second to the sixth year seldom under 5,900,000. Since 

 the volume of a red cell measures 0.000000072 cu. mm. and its surface 

 0.000128 sq. mm., the total surface of the red blood corpuscles present 

 in 1.0 cu. mm. of blood, must equal 640 sq. mm. Moreover, if the 

 blood contained in a mammal is calculated at ^{3 of its body weight, an 

 individual weighing 70 kg. must contain about 5 kg. of blood. The 

 body as a whole, therefore, gives lodgment to about 25,000,000,000,000 

 red cells, possessing a total surface of 3200 sq. mm. which equals an area 

 1500 times greater than that of the surface of the body. 1 These figures 

 clearly betray the surprisingly large size of the "breathing surface" 

 which the red corpuslces present to the air in the lungs or to the cells 

 of the tissues. 



Variations in the Number of the Red Blood Corpuscles. While 

 the value of 5,000,000 cells to the cubic millimeter of blood remains 

 fairly constant under normal conditions, it is subject to certain minor 

 fluctuations. Ordinary physical influences, for instance, possess 

 the tendency of diverting the corpuscles into the larger vascular chan- 

 nels, while the blood in the peripheral vessels contains them in some- 

 what smaller numbers. This fact should be taken into account when- 

 ever these bodies are counted in accordance with the method previously 

 described. It is also to be remembered that a diminution in the quan- 

 tity of the body-fluids may result at any time in consequence of a 

 lessened intake of water, or on account of a more copious discharge of 

 it in the sweat, stools or transudations. In either case, the number of 

 corpuscles per unit of blood must become greater. The reverse result 

 is obtained if large quantities of water are taken in, or if smaller 

 amounts are excreted. In early fetal life the red cells are fewer in 



1 Recent investigations have shown that in man the total amount of blood 

 should be calculated at one-twentieth of the body weight. The total surface of 

 the red cells, therefore, measures 1700 sq. mm. 



