148 THE BLOOD 



Fibrin may be separated out also by whipping shed blood with a stick. 

 After this operation the blood remains fluid, the fibrin having been collected 

 in the form of a white, stringy mass on the stick. 



1. THE AMOUNT OF BLOOD IN THE BODY 



The method of determining the amount of blood in the body is in brief 

 as follows: a normal sample of blood (b) is first drawn; then the animal is 

 bled and the vascular system is washed. out with water until the water flows 

 out perfectly clear. The water and blood are added together and the total 

 quantity designated w. The normal sample of blood is now brought by addi- 

 tion of water v to the same color as a sample of w. Then if we designate 

 by y the amount of blood washed out, it is evident that b : b + v : : y : w. From 



b X ^ 

 which y = j- The total quantity in the body is therefore b + y = b -|- 



"b X w 



- (Welcker). This method is not, however, quite exact, for after the 



o f v 



washing there still remains in the organs from eight to sixteen per cent of 

 the total hemoglobin. 



The amount of blood determined in this way amounts to seven to nine 

 per cent of the body weight in the dog, five to nine per cent in the rabbit (in 

 the latter after removal of the intestinal contents). Bischoff found in the 

 dead bodies of two executed criminals the quantities 7.1 and 7.7 per cent of 

 the body weight. 



2. THE FORMED CONSTITUENTS OF THE BLOOD 



A. THE RED BLOOD CORPUSCLES 



In most mammals the red blood corpuscles are thin, flat, slightly bicon- 

 cave, circular disks, composed of a soft, extensible and very elastic substance. 

 By transmitted light the color in thin layers is yellowish green; in thick 

 layers, red. In birds, reptiles, amphibia and most fishes, as well as in the 

 camel family, they are oval instead of circular. In the cold-blooded animals 

 and in birds they have a nucleus: in the mammals no nucleus is present in 

 the mature form of the corpuscle (cf. page 17). 



The diameter of the red blood corpuscle in man is 0.007-0.008 mm., its 

 thickness about 0.0016 mm. The volume of a single corpuscle, according to 

 Welcker, amounts to 0.000000072 cu. mm., and its surface to 0.000128 sq. 

 mm. One cu. mm. of human blood contains about 5,000,000 red corpuscles 

 for man and about 4,500,000 for woman. The total surface of the red cor- 

 puscles in 1 cu. mm. of blood therefore amounts to 640 sq. mm. in man and 

 576 sq. mm. in woman. Since the total mass of the blood in man is about 

 seven per cent of the body weight, i. e., in a body weighing 70 kg., about 

 5 kg. in round numbers, the total number of red blood corpuscles in a man 

 is 25,000,000,000,000, and their total surface 3,200 sq. m. (= 0.8 acre nearly). 



