[ 325] REPRODUCTION AND GROWTH OF MICE OF THREE STRAINS, AFTER TRANSFER TO- 3 ° C.

'Wild * house mice (Mus musculus L.) breed in cold stores kept at about —10 ° C (Laurie, 1946), and laboratory mice of the same species can be bred at an environ-mental temperature of — 30 C, given nesting material (Barnett & Manly, 1954; Barnett, 1956). The response of mice to low temperatures varies with different inbred strains. The differences are reflected in mortality (especially of young), growth, numbers of young born and weaned, and in internal, especially endocrine, changes. All these, and other aspects of the maintenance of the lives of mice at low temperatures, are to be discussed in future communications. This paper deals with the effect of low temperature on the reproduction of mice of three strains. The experimental mice were transferred as young adults from a 'normal ' temperature of about 210 C. to 10 ° C, or to — 30 C, and mated at the same time. The study of the reproductive performance and growth of these mice provides a quantitative expression of differences between the strains