Exposure to cold has been found to prevent liver necrosis in rats fed on a proteinpoor, sucrose-rich diet deficient in vitamin E (Naftalin, 195 I ) , to inhibit accumulation of fat in the liver in choline deficiency (Sellers & You, 1949,1952Treadwell, Flick & Vahouny, 1957), and to accelerate liver regeneration after removal of the left and median lobes (Moss & Weiss, 1955). In the study of Treadwell et al. (1957) growth rate and efficiency of protein utilization of rats fed on a diet with 5 or 10 % protein were found to be better in the cold ( I " ) than at 25', the reverse obtaining with diets containing 20, 30 or 40 % protein. When adult rats were fed on a diet containing 5 % casein, and immature rats on one containing 10 %, the survival rate was 75-87 % in the cold, whereas at 25' all animals survived. Meyer & Hargus (1959) noted that on a diet with 10 % casein rats gained more weight in the cold (2') than at 26O, whereas the reverse was observed when the diet contained 25 % casein.An increase in the energy expenditure, such as that which occurs in cold environments, does not necessarily mean that protein requirements simultaneously increase (Speck, 1860; Pettenkofer & Voit, 1866). Exposure to cold (5') increases calorie intake about twofold in the rat (Andik & Donhoffer, 1957); it would therefore be expected that the protein content of the diet that meets energy requirements in the cold would be less than that of a diet needed to meet energy requirements at higher temperatures. Consequently, it has been postulated that a marginal content of protein could be found, insufficient to secure survival at room temperature, but permitting survival in the cold because the increased food consumption would suffice to raise protein intake above the minimum subsistence level. Our investigation was designed to put this view to the test.
EXPERIMENTALMale albino rats of the Institute's colony, aged 9-1 I weeks at the outset, were used.Two groups of ten animals served to establish the growth rate at room temperature on diets containing 22 and 6.2% protein. The rest (thirty-five animals) received a diet containing 4-3 % protein and were kept at room temperature for 3 weeks; eighteen were then transferred to a large refrigerator and seventeen remained at room temperature; both groups continued to feed on the diet containing 4'3 yo protein. The rats in the refrigerator remained in the cold, after the death of the animals kept at room temperature, for at least another 10 days and in some instances for 21 days and were then returned to room temperature without change of diet. The experiments were spread over a year. The rats were divided into groups of six to eight and housed in available at https://www.cambridge.org/core/terms. https://doi
