398 



PRACTICAL PHYSIOLOGY 



the blood : 1-25 x 14 = 18'5 O 2 per cent. This agrees with the volume 

 of O 2 that can be extracted with the gas-pump. The co-efficient of 

 absorption of blood, neutralised by tartaric acid, and exposed at body 

 temperature to an atmosphere of CO 2 , is about 1. The tension of CO., 

 in the tissues is only about 5 per cent, of an atmosphere. One vol. of 



PIG. 258. Ferricyanide method of estimating the amount of O^ in blood. 23 

 C.c. of blood saturated with O a +30 c.c. of 1/500 ammonia solution are placed 

 in the bottle C. 4 c.c. of sat. sol. potassium ferricyanide in the tube A. After 

 mixing the gauge is brought back to its previous level by adding cold water to 

 A, and then the volume of O 2 is read in the burette. 



blood could at this tension take up by simple absortion only -^ of the 

 above, i.e. 5 vols. per cent. The C0 2 must therefore be chemically 

 combined. On breathing an atmosphere of C0 2 the blood may take 

 up 150 vols. per cent, owing to the high co-efficient of absorption (100 

 vols. absorbed and 50 vols. combined). 



From blood the whole of the C0 2 is set free in the gas pump, but in 

 the case of serum part of the C0 9 is fixed and is only set free after the 

 addition of an acid. The red corpuscles apparently play the part of an 

 acid. About one-third of the CO 2 is carried by the corpuscles, the rest 

 by the serum. Serum contains a larger quantity of C0 2 than an equal 

 quantity of blood. According to Bunge 1000 grms. of dogs' serum 

 contains 4-341 grms. sodium, of which 3-463 is sufficient to saturate 

 the chloride. The remainder, 0-878 grms., can combine with -623 

 grms. C0 2 to form sodium carbonate, and in addition with an equal 



