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Hormesis
Chester M. Southam and his colleague, John Ehrlich, described hormesis in their 1943 article titled the “Effects of Extract of Western Red-Cedar Heartwood on Certain Wood-Decaying Fungi in Culture.” This paper examined the differential growth rates of varying species of fungus. In solutions containing low concentrations of red-cedar heartwood, Southam and Ehrlich observed that the growth rate initially increased. However, the rate of fungi growth eventually slowed to stabilize the fungi concentration, mimicking a logistic function.

This experiment was significant because it contributed to studies involving dose-response relationships in which researchers use hormesis to explain why low concentrations of a substance result in positive effects, while higher exposure to the same substance is deleterious.

Transplantable Renal Tumor of the Rat
Southam experimented on rats and mice in order to observe the effects of injecting cancerous tumors into healthy subjects. In a 1960 paper titled “Transplantable Renal Tumor of the Rat,” Southam explains the details of his experiment in which he injected tumor cells into healthy rats. He first injected only newborn rats, but eventually experimented on rats of all ages. Additionally, Southam varied his solutions, injecting some rats with over 100 million tumor cells and others with 10 million tumor cells. At the time of the paper’s publishing, he had injected the tumor for eight generations.

In his paper, Southam describes the differences in tumor formation depending on the solution used. Rats injected with the larger dose had noticeable tumors by two weeks, while those injected with the lower, 10 million cell dose did not have apparent tumors until four weeks after the injections.

Furthermore, Southam examined the variety of tumor growth rates in his subjects. While tumors formed in 40-50% of all of the rats, their growth was fastest in rats less than 2 weeks old. These rats had evident tumors 2 to 3 weeks after the injections and died after 2 to 6 weeks. However, in adult rats, the tumor growth was slower on average, and most did not die for over 8 weeks after the injections.

Lastly, Southam observed how the rate of tumor growth depended on the transplantation generation. In the later generations, the tumors grew somewhat faster in younger rats than those from earlier generations. He also noted that the tumors appeared nearly identical to the original tumor, aside from slight structural differences.