ESTIMATION OF THE RED CORPUSCLES 24; 



tion of the red corpuscles is necessary, and the result is to 

 be considered in connection with the percentage of haemo- 

 globin. The colour-index, or index of corpuscular richness, 

 is the figure which indicates the richness of each corpuscle 

 in haemoglobin, the normal figure being unity. It is obtained 

 by dividing the amount of haemoglobin by the number of 

 corpuscles, each being expressed as a percentage of the 

 normal amount. In health there are 5,000,000 red cor- 

 puscles = 100 per cent, of normal, and 100 per cent, of haemo- 

 globin. The index is therefore : 



100 

 100 ~ 



If we found a case in which the red corpuscles were 

 4,000,000 (=80 per cent, of normal) and the haemoglobin 40 

 per cent., the colour-index would be : 



4 



- 



In another case we might find : Red corpuscles 1,000,000 

 (--=20 per cent, of normal), and haemoglobin 25 per cent. The 

 colour-index is : 



These figures would be suggestive of chlorosis and per- 

 nicious anaemia respectively. 



The percentage of red corpuscles is obtained from the 

 absolute count by multiplying the millions figure and the 

 hundred thousand figure by two (since the normal is 

 5,000,000, tlie said figures of which become 100 when multi- 

 plied by two). Thus, 2,500,000 = 50 per cent; 900,000=18 

 per cent., etc. The same rule may be used for women, for 

 the slightly lower normal total of reds is accompanied by a 

 smaller amount of haemoglobin. 



The following are the general rules (to which exceptions 

 are rare) for the interpretation of the colour-index : 



1. An index decidedly above unity indicates pernicious 

 anaemia, and usually in this disease the greater the anaemia 

 the higher the index. 



2. In chlorosis the index is greatly diminished : 0*2 has 

 been recorded, and the average is about 0-5. The exact 



