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A study was performed of the light transmission characteristics of the compressed "bloodless" ear in 70 subjects of white, Indian and Negro stock. It was found that in white children and adults of both sexes, the ratio of light transmission of the red filtered photocells to that transmitted to the infrared photocell was virtually constant when the ear was rendered bloodless by compression. The error introduced by assuming this ratio to be constant was no greater than the errors involved in making the measurement. If the assumption were made that this ratio was the same in Indian and Negro subjects as it is in white subjects, the estimation of the ratio would be in error in the average Indian subject by approximately -3.38 per cent and in the average Negro subject by -4.73 per cent.