A New Method of Testing Antityphoid Serum

Abstract

Summary Our experiments have shown that the virulence titer of the living typhoid bacilli is very variable according to the strain and that no quantitative relationship exists between the virulence titer and the binding power with relation to the protective unit of antiserum. For this reason the lethal dose of the bacteria is not a reliable measure of a protective unit of an antityphoid serum. A reliable test of a bacterial antiserum can be made only through the use of a standard serum. Our new method of testing typhoid antisera is as follows: with the use of an arbitrary protective unit of antiserum (standard serum) the L+ dose of a typhoid culture is determined; with this L+ dose the serum to be tested is mixed in varying quantities; the largest amount of the serum which will just permit the death of a guinea-pig of 250 grams weight within twenty-four hours after the mixture has been injected into the peritoneal cavity is taken as the protective unit. The value of an antityphoid serum is expressed by the number of such protective units contained in 1 cc. of the serum. Any strain of typhoid bacteria can be used for the test. The virulence control is not important. It is also unnecessary to attempt to increase the virulence of the cultures. Efforts in this direction have failed in our hands. The general adoption of our method and particularly of our protective unit will naturally permit, for the first time, a quantitative comparison of the antityphoid sera prepared with different strains and in various laboratories.