ORGAN WEIGHTS AND BODY COMPOSITION OF PARTURIENT AND LACTATING MICE, AND THEIR YOUNG, AT 21 C AND -3 C

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Abstract
Summary. Four classes of A2G/Tb mice were studied: (i) controls kept in an environmental temperature of 21° C; (ii) mice transferred at mating from 21 to −3° C; (iii) mice of the first generation reared at −3° C; (iv) mice of the twenty-fifth to the twenty-ninth generations of a stock kept permanently at −3° C. Of each class, some were killed, with their litters, at either first or second parturition, and some on the 10th day of either the first or second lactation. Litters kept for 10 days were reduced to four young at birth. The females at their first parturition were compared with virgins of a previous study. Pregnancy was accompanied by increase in the relative weight of heart, liver and stomach, and in the length of the small intestine; but the small intestine lost weight, and there was no change in kidney weight. The percentage of collagen and calcium in the body declined, but the absolute amount of nitrogen in the body increased. During lactation, the liver and stomach, but not the heart, increased in relative weight still further; and the weight of the small intestine also rose. The percentage of fat and calcium in the body declined. The relative weights of the heart, kidneys and small intestine were higher in the cold environment than at 21° C, but liver weight was not affected. The proportion of fat, nitrogen and collagen in the body was lower in the cold. The young had a much higher proportion of fat in their bodies at 10 days after birth than the neonates. They also contained more collagen and calcium and less water per unit body weight. The main effect of cold on the young was a higher fat content at birth.

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