An inquiry into the influence of the constituents of a bacterial emulsion on the opsonic index

Abstract

In preparing an emulsion of bacteria for opsonic estimations it is necessary to break up the masses so far as possible into their constituent bacterial elements and then to separate these from any clumps by centrifugalisation. The rate at which the suspended particles of an emulsion settle depends not only on the centrifugal force applied, but also on the fineness of the particles, and therefore on the efficiency of the method of breaking up the masses. If this is not efficient the suspended matter will fall in the form of coarse particles, leaving a relatively clear supernatant fluid containing very little in suspension. In the case of a tubercle emulsion we find that the best results are given by triturating a small quantity of dried bacilli with a pestle and mortar of which the grinding surfaces have the same curvature; using these, five minutes’ grinding is ample. The mass of dried bacilli is first ground up in the dry state and then made into a paste with a little 1-per-cent. saline (the strength used in all our experiments). The crude emulsion is then made by taking up the paste with 1 to 1½ c. c. of saline. When this emulsion is thoroughly centrifugalised it separates out into a deposit and an opaque supernatant fluid which is practically free from bacilli but which contains a considerable amount of bacterial detritus. If this supernatant fluid be pipetted off and the deposit again mixed with fresh saline and thoroughly centrifugalised, the second supernatant fluid will contain much less detritus and will be correspondingly clearer. By repeating this process several times it is possible to get a supernatant fluid which is almost clear and free from detritus. The deposit will then consist wholly of washed bacteria.