Further note on the influence of cholesterol on the growth of tumors

In previous papers it has been shown by Robertson and the writer, that cholesterol accelerates the growth of carcinoma in rats, and also, in view of the recent work of Wacker and of Ellis and Gardner, it may be a factor in the incidence of cancer. 1 In our original experiments the cholesterol was injected into, or around the tumor, and the criticism has been made, and justly too, we think, that the increase in the growth of the tumor might be due to the mechanical irritation of the injections, although we had previously controlled this possibility by injections of a balanced salt solution. We determined to test this matter further by making the injections on the opposite side of the body to that of the inoculations, and it has been the privilege of the writer to carry on these experiments in the absence of Robertson on sabbatical leave. Two sets of experiments were made, and may be briefly described.

Experiment 1.—Seventeen rats that had proved refractory to inoculation in April last (1913) were injected with 1 c.c. of a 2 per cent. emulsion of cholesterol in sodium oleate, on August 4 and 6, 1913. The injection was made on the left side. On August 6 they were all inoculated on the right side with the eighth generation of a Flexner-Jobling tumor. The injections of cholesterol emulsion were continued every alternate day thereafter, on the left side. On August 27, twenty-one days after inoculation, eight rats had developed tumors, ranging from 5×5 mm. to 13×15 mm. in size, the average for the eight being 9.7 mm. Bearing in mind that rats previously refractory may later become susceptible, and that tumors vary in virulence, this is not conclusive.