1. Some strains of Trypanosoma lewisi may, at times, produce rapidly fatal infections in a large percentage of the rats infected.

2. In such strains of Trypanosoma lewisi, a sufficient degree of pathogenicity may persist to warrant the designation of these strains as pathogenic.

3. The pathogenicity of a given strain of Trypanosoma lewisi is not constant, but is subject to marked and even sudden variations.

This content is only available as a PDF.