272 THE INCOME OF ENERGY 



so that the hsemoglobin is thoroughly saturated 

 with carbon monoxide and the full pink tint 

 of the CO-hmoglobin appears. Then add water 

 drop by drop from a pipette until the tint in 

 the graduated tube equals that in the standard 

 tube. In comparing the tints of the two tubes, 

 it is best to hold them up against the light from 

 the sky. The precaution must always be taken 

 of repeatedly transposing the tubes from side to 

 side during the observations : otherwise very 

 considerable error may arise. The percentage 

 is read off on the tube after half a minute has 

 been allowed for the liquid to run down. An- 

 other drop is now added, and if necessary another, 

 until the tints again appear unequal. Usually 

 the tints will appear equal for two or possibly 

 three additions. The mean of the readings which 

 gave equality is taken as the correct result. The 

 results in successive experiments with the same 

 blood should agree within one per cent of the 

 mean. 



The average percentage of haemoglobin in the 

 blood of women is 11 per cent, and in the blood 

 of children 13 per cent below that of adult men. 

 In calculating the proportion of haemoglobin in 

 the blood of women and children as percentages 

 of the average normal proportion, it is evidently 

 necessary to add about one-eighth for women 



