The thymidine incorporation inhibiting screening system (TSS) to test carcinogenic substances (a nuclear DNA...

Suckling mice of the same litter served as test animals. One half received the test substances by i.p-injection, the other half (control) was applied the solvent only. The suppressive effect of carcinogenic substances on nuclear DNA synthesis in tubular renal and in liver epithelia was ascertained in autoradiographs by silver grain counting. The decrease of the mean of silver grain number over the nucleus served as a criterion for the suspicion of carcinogenicity. Non carcinogenic chemicals did not causes this suppressive effect.