An improved method for opsonic index estimations, involving the separation of red and white human blood corpuscles

Abstract

Opsonin is the name given by Sir A. E. Wright to the substance in human blood which mainly influences phagocytosis. In order to measure the opsonin, equal volumes of normal serum, of a bacterial emulsion, and of leucocytes are incubated to promote phagocytosis, and the number of bacteria visible in a random sample are counted in a stained film preparation. By repeating the experiment with a pathological serum, a ratio is obtained which is known as the opsonic index. The method, however, has been found inaccurate, and consequently fallen almost into disuse. Drs. Greenwood and White pointed out the error of random sampling and, after elaborate mathematical analysis, adjudged the “liability to error” on a single count to occasionally exceed 20 per cent, from the mean or true figure. Clearly, when the counts from two films are contrasted, the liability to error may be doubled. This liability to error is due to the variation in content of different leucocytes in the same film ranging from 0 to 25 bacteria, and the resulting total in 50 leucocytes will vary according to the field in which the operator happens to make his count, i. e ., one rich in high or low contents.