ADVANCED DEMONSTRATIONS 



409 



The subject then begins to breathe from the bag, oxygen being 

 supplied as required. The required volume of CO (about 130 to 

 150 c.c.) is driven into the bag 30 c.c. every two minutes. After the 

 last of the CO has been washed into the bag the subject continues to 

 breathe in and out of it for about 3'. A sample of his blood is then 

 taken. 



FIG. 264. Haldane's apparatus for determining Og tension in human blood. R, T, C, 

 apparatus for delivering CO at measured rate ; M, mouthpiece ; V, valves made of pieces 

 of intestine ; B, air-bag for controlling pressure during expiration ; G, metre. 



The volume of dry CO, reduced to and 760 mm., is then calcu- 

 lated. From this volume and the percentage saturation of the blood 

 the volume of CO or of O 2 capable of being taken up by the whole 

 blood is calculated. 



Example : Supposing the vol. of CO taken up is 150 c.c., and the 



saturation of the blood sample with CO equals 25%, then the CO (or 



1 f\r\ 

 oxygen) capacity of the total blood is 150 x -^ = 600 c.c. 



From .the total and percentage 2 capacities of the blood the total 

 volume is calculated. 



100 

 Supposing the percentage 2 capacity is 20, then 600 x -^- = 3000 c.c. 



To obtain the mass x by 1'05 (the specific gravity of blood) = 3165 grms. 

 The average weight of blood in man was found to be ~^?\ of the body 



weight. In a fat man it was -^. 



In chlorosis, the total amount of haemoglobin in the body is not 



