A precipitating and neutralizing antistreptococcus (scarlatinae) horse serum.

The immune serum, used in the experiments to be reported, was prepared in the horse (Horse 10) by repeated inoculation of hemolytic streptococci freshly isolated from the acutely inflamed throats of three typical cases of scarlet fever. The injections were made intravenously on three successive days each week from December 19, 1917, to April 20, 1918. The initial injection consisted of the heated (56° for forty-five minutes) bacteria from 100 cc. of glucose broth, suspended in 10 cc. of sodium chloride solution. The heat-killed organisms were injected during the first five weeks, and live bacteria during the remainder of the period of immunization. The dose was gradually increased until the organisms from 600 cc. of broth were given at a single injection. The horse remained well until the latter part of March, when it developed arthritis which gradually increased until May 6, when it was bled to death under anesthesia. The serum used was obtained from this bleeding and from bleedings made April 8 and May 1. After the serum had been proved sterile, 0.2 per cent tricresol was added, and the serum placed in amber bottles securely stoppered and kept continuously in the ice chest.

Another horse (Horse 19), whose serum was used as a control, was immunized in a similar manner but with hemolytic streptococci from septic infection.