With the recent development of technics [sp] for transplanting human tumors to the cheek pouch of.cortisone-treated hamsters, it has become possible to test the response of human tissues under the conditions of hibernation. During the past year we have tested five transplantable human tumors. Our results indicate that the growth of this tissue from a homeothermic mammal is markedly inhibited by hibernation, but that the tumor survives after prolonged exposure to these low temperatures. Our primary reason for carrying out this study was to test the possibility that the growth rate of these heterologous tumors might be slowed down sufficiently to provide a means of temporarily "storing" transplantable human tumors.
Natural hibernation is contrasted with induced hypothermia, one of the major differences being that the process of hibernation is physiologically controlled and regulated while hypothermia is a breakdown in temperature regulation causing a weakening or collapse of other homeostatic m.echanisms. As a demonstration of the remarkable control and regulation evinced in natural hibernation, the process of entering the hibernating state is investigated. In hibernation, the process is passive, wjth declines in respiratory rate, heart rate, and oxygen consumption preceding the drop in body temperature; in enforced hypothermia the animal chills in spite of a violent metabolic effort to remain warm. This control is demonstrated throughout hibernation; between ambient temperatures of about 4° and 15°C, the animal passively follows the environment, but if the temperature goes below 0°C the metabolic rate is increased and body temperature is maintained above freezing. The circulatory process in the aro)lsing hibernator is followed. The arousing hibernator1 s circulatory control and ability to rewarm are in strong contrast to the animal undergoing induced hypothermia; in hypothermia almost all ability to rewarm is lost. It is shown that the hibernators have a specialization of temperature control which is unique among the vast array of mammals. However, the precise nature of the changes made during this resetting of the "physiological thermostat" is largely a mystery.
Body temperature and oxygen consumption were measured at various environmental temperatures in a series of captive and wild caught vampire bats, Desmodus rotundus. The response to changes in ambient temperatures was unpredictable and could not be correlated with the age or sex of the animals, their nutritional condition, or the length of their captivity. Body temperature varied greatly, but generally did not fall below 30° C when the ambient temperature was above 25° C. At lower ambient temperatures, some bats increased their metabolism and maintained a high body temperature for varying periods, while others showed little or no increase in metabolic rate, and their body temperatures declined. Below about 20° C body temperature, bats were unable to rewarm themselves without exogenous heat. Calculations indicate that vampires did not drink sufficient blood to maintain a homeothermic condition at the temperatures of temperate zone hibernacula. Bats could tolerate ambient temperatures of 33° C or more for only short periods. It is suggested that Desmodus is limited from spreading northward because of its inferior temperature regulation.