Abstract
We have elsewhere shown 1 that cholesterol, when injected directly into rat carcinomas, causes a marked acceleration both of the primary and of the metastatic growth of the tumors.
This led us to form the opinion that cholesterol is probably a factor of importance in determining the incidence of carcinoma.
It has been shown by Dorée and Gardner, Ellis and Gardner, and others 2 that cholesterol is not synthesized by animals, the cholesterol in animal tissues being derived from their diet. This fact suggested the possibility that the incidence of carcinoma in inoculated animals might be diminished by feeding them for a considerable period prior to the inoculation upon a diet poor in cholesterol.
Accordingly twenty-two white rats, about two months old, were divided without exercising any selection into two lots. One lot of 15 were fed upon a diet composed exclusively of milk; the remainder were fed upon a mixed diet of oats and meat.
The content of cholesterol in milk, while by no means negligible, is extremely small in comparision with the content of cholesterol in other foodstuffs. Thus Tolmatscheff finds that human milk contains from 0.025 per cent. to 0.039 per cent. of cholesterol, 1 while Bömer and Kirsten find that the fats in cow's milk contain 0.5 per cent. cholesterol, corresponding to a content of less than 0.02 per cent. in the whole milk. 2 Meat, on the other hand, contains from 0.07 to 0.08 per cent. of cholesterol, 3 while the content of phytosterols in seeds is considerable. 4
Both lots of animals thrived well, the milk-fed animals presenting an especially well-nourished appearance.
At the end of two months both lots of rats were inoculated in the axillary region with portions of a Flexner-Jobling carcinoma. The diet of each lot of rats was maintained unaltered. At the end of twenty days the proportion of successful inoculations in each batch of animals was determined, with the following results:
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