Abstract
In continuation of the experiments reported previously, 1 , 2 , 3 Berkfeld filtrates from broth cultures of tubercle bacilli were used in the systematic immunization of a sheep. These toxin filtrates, hereafter designated as T. F., were obtained by growing a virulent strain of human tubercle bacilli in glycerinated “hormone broth” for 18 to 21 days and filtering the culture through a Berkfeld “N” candle. The sheep was injected subcutaneously at weekly intervals with increasing doses of freshly prepared filtrate. After four months, neutralizing properties of the serum were studied by the intracutaneous and intraperitoneal method in tuberculous and normal guinea pigs, and by skin tests in tuberculous and non-tuberculous human subjects.
Having found previously that an intracutaneous injection of unheated T. F. in the experimental tuberculous animal caused a definite skin reaction, the effect of an incubated mixture of immune sheep serum and T. F. was now studied.
Intracutaneous Method. Series of four guinea pigs each were infected with human tubercle bacilli, respectively 3 and 9 weeks and 3 and 5 months before these tests were made. Intracutaneous injections were given of a mixture of equal parts of serum and T. F., T. F. in a dilution of 1 :2, immune serum alone, a mixture of normal sheep serum and T. F., and a mixture of immune rabbit serum and T. F. The dose, 0.05 cc., was injected after incubating all of these materials for one hour at 37.5° C. on a water bath. The results showed consistently that immune sheep serum (or immune rabbit serum) prevented the occurrence of positive skin tests, whereas normal sheep serum or normal rabbit serum failed to do so. Positive reactions were characterized by an area of redness and deep induration varying in extent from 0.5 × 0.5 to 1.5 × 1.5 cm. and lasting several days.
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