BIOCHEMICAL FACTORS IN THE MAXIMAL GROWTH OF TETRAHYMENA

¹ Arnold Biological Laboratories, Brown University, Providence, Rhode Island

1. The known growth promoting substances alone or in various combinations are not sufficient for the growth of Tetrahymena geleii at a maximal rate and density.

2. At least two unknown substances (factor I and factor II), present in both plant and animal materials, are required for such growth.

3. Factor I is distinguished from factor II by the fact that the former is precipitated by heavy metal salts while the latter is not.

4. Active protein-free preparations of these factors may be prepared from extracts of timothy hay by treatment with ethyl alcohol.

5. Growth of the ciliate could not be obtained in acid digests of casein or in solutions of free amino acids supplemented with the protein-free extract.

6. Tyrosine, valine, and isoleucine were found to be inhibitory in the presence of gelatin, but not in the presence of casein.

7. A large increase in the population density occurred in the presence of tryptophane and gelatin but not with tryptophane and casein.