CH. XXVI.] THE QUANTITY OF BLOOD 411 



Haldane and Lorrain Smith have recently investigated the ques- 

 tion by another method. The data required are (1) the percentage of 

 haemoglobin in the blood, and (2) the extent to which the haemo- 

 globin is saturated by a measured amount of carbonic oxide absorbed 

 into the blood. 



The percentage of haemoglobin is determined colorimetrically by 

 the Gowers' or Gowers' -Haldane haemoglobinometer (see p. 438). In 

 the latter instrument the standard 100 per cent, of colour corresponds 

 to a capacity of 18'5 c.c. of oxygen or carbonic oxide per 100 c.c. of 

 blood. The subject whose blood is to be measured breathes a known 

 volume of carbonic oxide, and a few drops of the blood are taken and 

 the saturation of his haemoglobin is determined colorimetrically. 

 From this result the total capacity of the blood for carbonic oxide is 

 calculated. The "carbonic oxide capacity" is the same as the 

 " oxygen capacity." The volume of the blood is then calculated from 

 the total " oxygen capacity," and the percentage capacity as deter- 

 mined by the haemoglobinometer. The following is an example : The 

 subject's blood in a given case has, let us say, the colour of the 100 

 per cent, standard, and therefore has a capacity of 18*5 c.c. per 100 

 c.c. blood. He is then allowed to breathe 75 c.c. of carbonic oxide, 

 and it is then found that his blood is 15 per cent, saturated. The 

 amount required to completely saturate his blood, or in other words 



his total capacity, must be 75 x ---=- = 500 c.c. Since 18*5 c.c. of this 



1 o 



total is carried by 100 c.c. of his blood, the total volume required to 

 contain 500 c.c. is 500x^-^ = 2700 c.c. The subject has therefore 



-Lo O 



2*7 litres of blood. The total weight is obtained by multiplying the 

 volume by the specific gravity (about TO 5 5). 



Some of the results of this method are as follows : The mass of 



the blood in man is about 4 - 9 per cent. (^TT^ ) of the body- weight. 



' 



The corresponding ratio of the blood volume is 4 - 62 c.c. per 100 

 grammes or 7^-7. The commonly accepted estimate of the mass of 



the blood is thus too high. In pathological conditions the numbers 

 are different ; thus in anaemia from haemorrhage, the volume ratio is 

 6*5, in pernicious anaemia 8'6, in chlorosis 10'8. In other words, in 

 various forms of anaemia the actual volume of the blood is increased. 

 Prof. Lorrain Smith has pointed out to me that the decapitated 

 criminal investigated by Weber and Lehmann mentioned above, 

 suffered from scurvy, a disease which is accompanied by anaemia ; 

 hence the total volume of his blood was pathologically high. 



