Large forms of histoplasma

Summary Various types of large forms ofHistoplasma were studied in experimentally infected hamster and mouse tissues.Histoplasma can be found in the yeast phase in 5 distinct forms: 1. the classicalHistoplasma capsulatum form (ovoid, 2–5 µ in size); 2. occasional large forms in necrotic tissue and old cultures (up to 9 µ); 3. induced large forms in tissue explants (up to 20 µ); 4. small or large yeast cells surrounded by halos (up to 30 µ) and 5. the duboisii form (up to 22 or more) found exclusively inHistoplasma duboisii. Correlations between the above large forms with the classical small form were discussed.Histoplasma duboisii and the classicalHistoplasma capsulatum can be separated (1) by its size in the parasitic phase in vivo and in vitro; (2) by its different pathogenicity for experimental animals and (3) by the most particular tissue response in hamsters and in mice.This project was in part supported by Research Grant E-576 of the National Institutes of Health and a grant of the Squibb Institute for Medical Research.