1. In June 1952, two strains of virus were isolated with mice from two out of seven blood samples of epidemic hepatitis. One of them from a moderate case of epidemic hepatitis has passed 24 generations and revealed no sign of attenuation up to the present. The other from a light case is not yet well fixed.
2. The first strain of virus that was isolated from the liver of a severe case of epidemic hepatitis in February 1952, has passed 54 generations and revealed no sign of attenuation up to thee present.
3. All these three strains cause severe changes of typical viral hepatitis in mice.
4. The two strains (the first and the second) which have been well fixed, reveal the similar particles in the electron-microscopic photographs. They are round and 100-150mμ large.
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