Abstract
The agglutination of bacteria may be regarded as a precipitin reaction at the surface of the cells. 1 , 2 A method had been worked out in this laboratory for the quantitative estimation of precipitins, 3 and it has been found possible to adapt the procedure to the micro determination of agglutinins. Thoroughly washed, heavy bacterial suspensions are standardized by measuring their nitrogen content per cc. by the micro-Kjeldahl method. Accurately measured quantities of bacteria and an appropriate antibody solution or serum are then mixed and allowed to stand, with occasional mixing, at 37° for 2 hours and overnight in the ice-box. The remainder of the analysis is carried out as in the precipitin reaction, 3 except that it has been found convenient to make use of the higher speed possible with the angle centrifuge.† This was run in an ice-box compartment. Agglutinin nitrogen is determined by subtracting from the total nitrogen of the washed precipitate the amount of nitrogen contained in the bacteria used. Agglutinin N may also be determined from the difference between a blank without bacteria, and the supernatant from the agglutination. Both methods are illustrated in Table I. Agglutinin — agglutinin N × 6.25, under the assumption that agglutinin is protein. If the relative amounts of bacteria and serum are so chosen that the supernatant contains no more agglutinin the result obtained (divided by the volume) is the agglutinin content of the serum in milligrams per cc. In the table are given typical data for pneumococcus agglutinins. Application of the method to other systems is in progress.
An immediate outcome of the method is given in the following notice. Quantitative evidence bearing on the mechanism of bacterial agglutination has also been obtained, and will be published later.
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