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William G. Exton, M.D.
JAMA. 1930;94(20):1573. doi:10.1001/jama.1930.27120460004010d.
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Notwithstanding improvements in hemacytometers and photographic methods,1 red blood cell counting is usually regarded as the most tedious of all routine clinical pathologic procedures. It is, however, an easy matter to count red blood cells by measuring their turbidities in suspensions, and counts made by scopometry2 are in excellent agreement with hemacytometer counts on the same specimens, as shown in the accompanying chart.

To count the red cells, one should dilute the blood 1:1,000 with a solution consisting of 2 per cent sodium citrate and a diluted "solution of formaldehyde-U. S. P." (1:10), which keeps them in good condition at room temperature. To do this easily, the blood may be collected and. diluted 1:100 in the usual hemacytometer pipet and then diluted again 10 times. After gentle mixing, the turbidity of the sample is measured with the junior scopometer.3

The simple scopometer measurement wholly eliminates the microscopy


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