Of the attempts to isolate an antidiphtheria phage (1) from stools collected daily during the course of a case of the disease, (2) from a 33 day old broth culture of B. diphtheriæ, (3) from intestinal contents and peritoneal washings of guinea pigs inoculated with three different toxic strains of B. diphtheriæ, none yielded an antidiphtheria phage. However of eleven specimens of feces collected from eleven antitoxin horses one was found to contain a bacteriophage active against B. diphtheriæ. This phage was not observed in the first generation and did not show up until transferred the second time. Had the results of the first transfer been regarded as final in all certainty the existence of a phage would not have been recognized. Two additional specimens of feces from the positive horse (No. 156) were later tested to determine whether this bacteriophage was continually present in the intestinal tract of this animal. Both of these feces filtrates failed to yield a phage. Later a sample of freshly collected blood serum from the same horse was tested and found not to contain a phage.

The antidiphtheria phage was tested against eighteen non-diphtheria strains of microorganisms to determine whether it would show lytic activity for related or unrelated bacteria. There was no evidence of lysis in any of these types. The specificity of this phage was also tested on nine strains of B. diphtheriæ and found to be active on three heterologous strains (Strain M 1314, Strain F and Strain G). These incidentally were all recently isolated. It failed to lyse the remaining six strains of which five were recently isolated.

B. diphtheriæ Strain M 1314 was used in combination with nine heterologous bacteriophages isolated from various sources, to determine if any of these phages would by chance lyse this culture. The results were all negative.

To date this phage fails to show complete lysis although the twenty-second generation has a titer of 1 x 10–9.

Additional proposed experiments involving this phage are being planned and will be undertaken in the near future.

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