I50 BACTERIOLOGICAL DIAGNOSIS. 
scarcely necessary to say that they should not be 
counted. 
6. The calculation.—The best way of calculating the 
number of corpuscles present from the data thus 
obtained is the following :— 
First add up the number of corpuscles in all the 
squares which you have counted and divide the sum by 
the number of squares counted. This gives the average 
in each square. 
ApH > 
Fic. 24.—Showing method of counting red corpuscles: a, a, a, are 
counted in square A; 5, 6, in B; ¢, in C. 
Now the space enclosed between each square and the 
cover-glass above it is ~5 of a millimetre deep, 4, of 
a millimetre wide, and #, of a millimetre long; its 
cubic capacity is therefore 2, x gy X a = aos Of 
a cubic millimetre. Therefore the ggy5 part of a 
cubic millimetre contains the number of corpuscles 
which we have already found as the average. 
But the square contained diluted blood ; if the amount 
