ESTIMATION OF RED CORPUSCLES. I51 
of dilution was 1 in 100 the amount of blood contained 
in the space over each square was ;3, part of -d,, of 
a cubic millimetre. 
Therefore, the number of corpuscles which has been 
determined as being the average per square is contained 
in ggg Of zz Of a cubic millimetre of undiluted blood, 
the dilution being taken as 1 in 100. 
Hence the number of corpuscles in one cubic milli- 
metre of undiluted blood is obtained by multiplying the 
average per square by the number which expresses the 
dilution (in this case 100) and then by 4000. 
It may be expressed as a formula, thus:— 
If ~ is the total number of corpuscles counted, 
s is the number of squares counted, 
and if the dilution is 1 in d. 
Then the number of corpuscles per cubic millimetre 
a: 
is= x d X 4000. 
Example.—Suppose that we have counted 100 squares 
and have found that they contain 1200 corpuscles. 
Then the average per square is 12. 
Then z55 Of a cubic millimetre of diluted blood 
contains 12 corpuscles. 
Or, <$5 Of aoa Of undiluted blood contains 12 cor- 
puscles, supposing the dilution was 1 in 100. 
Therefore, one cubic millimetre of undiluted blood 
contains 12 X 100 x 4000 = 4,800,000 corpuscles. 
Or by the formula :— 
Number of corpuscles per cubic millimetre :— 
1200 
100 
The beginner is strongly advised to work out the 
problem at full length until he has become absolutely 
familiar with the reasons for all the steps. 
X 4000 X 100 = 4,800,000. 
