446 THE BLOOD [CH. XXIX. 



per 100 c.c. of blood, 15 per cent, of this 18-5 c.c. is present in the 

 form of carbonic oxide, 15 per cent, of 18-5= =. = 2-7 c.c. 



Now if 2-7 c.c. of carbon monoxide per 100 c.c. of blood is the result 

 of breathing 75 c.c. of that gas, the question before us is, How much 

 gas will be necessary to produce the normal figure 18-5 ? 



2-7 c.c. per 100 c.c. of blood results from breathing 75 c.c. of CO 



75_ 



. . X C.C. ,, f. j_ ,, 



75x18-5 

 and 18-5 c.c. ^7 



- 500 c.c. 



(approximately). 



In other words, the total oxygen (or CO) capacity of the person's 

 blood is 500 c.c. Since 18-5 c.c. of this total is carried by 100 c.c. 

 of blood, the total volume of the person's blood, that is, the amount 



which will contain 500 c.c. of gas, is ^-= = 2727 c.c., or nearly 



-Lo* 



three litres. The total weight of the blood is obtained by multiply- 

 ing the volume by the specific gravity (about 1-055). 



Some of the results of this method are as follows : The mass of 



the blood in man is about 4*9 per cent. ( ^-^ ) of the body- weight. 



' 



The corresponding ratio of the blood volume is 4'62 c.c. per 100 

 grammes, or -^ ^ In pathological conditions the numbers are 



different; thus in ansemia from hsemorrhage, the volume ratio is 6*5, 

 in pernicious anaemia 8*6, in chlorosis 10'8. In other words, in 

 various forms of ansemia the actual volume of the blood is increased, 

 but of course the corpuscular and solid constituents are correspond- 

 ingly diminished. 



Coagulation of the Blood. 



After the blood is shed it rapidly becomes more viscous and then 

 sets into a firm red jelly. The jelly soon contracts and squeezes out 

 a straw-coloured fluid called the serum. With the microscope, 

 filaments or fine threads are seen forming a network throughout the 

 fluid (fig. 317), many radiating from small clumps of blood-platelets. 

 These threads entangle the corpuscles, and so the clot is formed. 

 The threads are composed of a protein substance called fibrin, and 

 the formation of fibrin is the essential act of coagulation. Fibrin is 

 formed from the plasma, and may be obtained free from corpuscles 

 when plasma is allowed to clot, the corpuscles having previously 

 been removed by methods we shall immediately study. It may also 



