Responses to Hypothermia in Several Species of Infant Mammals

Abstract

Cat, golden ham-ster, rat, and to some extent mouse, guinea pig and rabbit, were studied at diverse postnatal ages. Low body temps, that were lethal became higher with increased age in all spp. In cat they rose from 7[degree] C to 18[degree]; in hamster only from 1[degree] to 4[degree]. Heartbeat frequencies (from electrocardiograms) were usually exponentially related to body temps. in infants, and linearly in adults except above 33". The transition from infant to adult occurred in at least two steps. Isolated perfused hearts manifested relations to temp. unlike those of the heart in situ, and showed less change with age. Breath frequencies decreased as body temp. decreased in newborn infants, but not in those more than 15 days of age. The adult pattern of responses to hypothermia thus emerged at the end of serial modifications, and in any one species each modification occurred at a specific age.