ESTIMATION OF THE RED CORPUSCLES 209 



It may be expressed as a formula, thus : 



If n is the total number of corpuscles counted, 

 s is the number of squares counted, 

 and if the dilution is i in d, 



then the number of corpuscles per cubic milli- 

 metre is - X «; X 4,000. 

 s ^' 



Example. — Suppose that we have counted 100 squares, and 

 have found that they contain 1,200 corpuscles, then the average 

 per square is 12. 



Then j^^ cubic millimetre of diluted blood contains 12 cor- 

 puscles. 



^'^' Tws of ^rxnJTT undiluted blood contains 12 corpuscles, 

 supposing the dilution was i in 100. 



Therefore i cubic millimetre of undiluted blood contains 

 12 X 100 X 4,000 = 4,800,000 corpuscles. 



Or by the formula — 



Number of corpuscles per cubic millimetre = 



1,200 n 



X 4,000 X 100 = 4,800,000. 



100 ^ ^ 



Where the dilution is i in 100 (as is recommended, since it 

 enables the red corpuscles and the leucocytes to be counted in one 

 specimen) the calculation can be simplified still further. Add 

 up the number of corpuscles in the hundred squares counted and 

 multiply by 4,000. If you count 200 squares, multiply by 2,000, 

 and so on. 



In a normal connt then are 1,250 in the hundred squares counted, 

 250 in each " har " of twenty squares, and 12^ in each small square, with 

 the dilution of 1 in 100. A knowledge of these facts will enable the 

 approximate condition of the blood to be obtained at a glance. 



The beginner is strongly advised to work out the problem at 

 full length until he has become absolutely familiar with the 

 reason for all the steps. 



Clinical Applications. 



As this is more tedious than the estimation of the haemoglobin, 

 and is really less important in the recognition of ansemia, it may 

 often be omitted in clinical work. When possible it should be 

 done, as it serves as a useful check on the results obtained by the 



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