BLOOD-VOLUME 21 



1. Haldane's Carbon-monoxide Method 



This method depends upon the fact that carbon monoxide 

 combines with haemoglobin to form a compound more 

 permanent and of a brighter tint than oxyhsemoglobin. 

 The following are the steps in the process- — 



1. The oxygen capacity of the subject's blood is first 

 determined — that is to say, the amount of oxygen with 

 which 100 c.c. of blood can combine. This is estimated 

 most accurately by an indirect method. The oxygen 

 capacity of ox blood is determined directly by the ferri- 

 cyanide method. By means of the heemoglobinometer, 

 the haemoglobin content of the ox blood and of the sub- 

 ject's blood are compared. From this is calculated the 

 oxygen capacity of the subject's blood. Suppose 1 c.c. 

 of blood combines with a c.c. of oxygen. 



2. The subject breathes a known volume (V) of carbon 

 monoxide. This turns out some of the oxygen from com- 

 bination with haemoglobin. 



3. The percentage saturation of the blood with CO is 

 determined in the following way. A sample of blood taken 

 before CO inhalation, (A), and a sample taken after, (B), are 

 diluted to the same amount. The latter will be sUghtly 

 redder than the former. Another sample (C), similarly 

 diluted, is saturated with CO by bubbhng coal-gas through 

 it. This, of course, will be redder still. Carmine is now 

 added to A from a burette until the colour is the same as B. 

 Let the amount of carmine used be x. Addition of carmine 

 is then continued until the colour equals that of C. Let 

 the total amount of carmine added be y. 



The amount of CO required to saturate the blood com- 

 pletely would therefore be - x V. Now a given weight 



of haemoglobin combines with the same volume of oxygen 

 as it does with carbon monoxide. The amount of oxygen 

 required to saturate the whole of the haemoglobin is there- 



