Our later investigations confirm our previous results.

1. It is possible to increase markedly the effect of substances inhibiting tumor growth by using certain combinations of these substances which, when given alone, have some effect on tumor growth.

2. Immunity acquired against the effect of these substances depends partly upon an active immunization of the tumor cells themselves against the action of these substances, and this immunity is transmitted to the following generations of tumor cells.

3. The immunity against the substances inhibiting tumor growth is, as far as we have investigated the problem, specific.

4. Our later experiments provide a more secure basis for the additional and more general conclusions which we mentioned tentatively in our previous paper.

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