THIS PAPER is concerned with an investigation of the innate mechanism of animals against cancer and an attempt to bring together the many theories regarding the causes of this disease.
It has been clearly demonstrated that the guinea pig normally possesses in its serum a powerful tumor inhibitory principle (TIP) against a variety of transplantable tumors.1. 5. 6 In attempting to isolate TIP we determined that it is not contained in erythrocytes or their products, that it is not a lipopolysaccharide, complement, or properdin, and that it is not extractable with dimethylformamide, acetone, or ether.5 Contrarily, we demonstrated that it is heat stable, that it is extractable with methanol, that it can be separated off by ammonium sulfate fractionation, and that it is associated with the globulin fraction of the serum. Examining physiologic saline extracts and ammonium sulfate fractions of such extracts of guinea pig muscle, lung, spleen,