RESPIRATION 427 



sumption. When, however, Douglas and Boycott made a number of de- 

 terminations with a much larger bag which necessitated continuation of 

 the breathing for a considerable time after the CO had been given, they 

 obtained higher average results for the blood volume in man than 

 Lorrain Smith and I had got. Douglas and I therefore reinvestigated the 

 question as to how long the CO requires to distribute itself equally, and 

 found that when the samples were taken only two or three minutes after 

 cessation of the administration of CO the percentage saturations of the 

 blood were from 10 to 25 per cent higher than 15 minutes later. After 

 10 to 15 minutes, however, the saturation remained constant if the 

 subject continued to breathe from the bag. Our original experiments gave, 

 therefore, results for the blood volume which were too low probably by 

 about 25 per cent. The average blood volume in man by the CO method 

 is about 6.5 to 7 per cent of the body weight, and the total oxygen capacity 

 of the haemoglobin about i.i to 1.3 liters per 100 kilos of body weight. 



It is probable that, as regards most of the circulating blood, mixture 

 with any added substance such as CO takes place very rapidly. In some 

 parts of the body, however, the circulation is so slow that a considerable 

 time is required for mixture. 



Douglas, 20 and also Boycott and Douglas 21 applied the above de- 

 scribed CO method to animals, and took the opportunity of comparing the 

 results with those obtained by the older colorimetric method of Welcker, 

 which can only be applied after death. The series by Douglas showed an 

 average difference of 3 per cent, and that of Boycott and Douglas of 

 +5-5 per cent with the CO method as compared with the Welcker method. 

 It is evident, therefore, that no substance except haemoglobin combines 

 with CO. It must be remembered, however, that many of the muscles 

 contain some haemoglobin, and that by both methods this small fraction 

 of the total haemoglobin is estimated as if it belonged to the blood. 



In using the CO method for human experiments it is necessary to 

 adjust the volume of CO administered to the patient's weight and prob- 

 able oxygen capacity, so that the percentage saturation of his haemo- 

 globin is not likely to rise above about 20; otherwise slight headache 

 may result. For persons of ordinary weight about 1 50 cc. of CO would 

 be suitable ; but in cases of pernicious anaemia or anaemia from loss of 

 blood, and in children or persons of low weight, far less CO should be 

 given. On the other hand in cases of polycythaema it may be necessary 

 to give 300 cc. or more in order to obtain a percentage saturation suffi- 

 cient for a satisfactory titration of the blood. As CO only leaves the 

 blood slowly when the percentage saturation is low, it is hardly neces- 

 sary, except in very exact experiments, to keep the patient breathing 

 from the bag after all the CO has been absorbed. 



20 C. G. Douglas, Journ. Physiol., XXXIII, p. 493, 1906, and XL, p. 472, 1910. 

 n A. E. Boycott and C. G. Douglas, Journ. Path, and Bact., XIII, p. 256, 1909, 

 and A. E. Boycott, same Journal, XVI, p. 485, 1911. 



