The blood-borne “trigger” for natural mammalian hibernation in the 13-lined ground squirrel and the woodchuck

A blood-borne trigger for natural mammalian hibernation is described and details of the conditions necessary for its successful utilization are enumerated: 1. It is present in serum and cells of hibernation blood both in ground squirrels (Citellus tridecemlineatus) and woodchicks (Marmota monax). 2. It acts intra and interspecifically insofar as appropriate hibernation serum of 13-lined ground squirrel when transfused can trigger hibernation in other ground squirrels of the same species, and appropriate hibernation serum of woodchucks can similarly trigger hibernation in both woodchucks and in 13-lined ground squirrels. Withdrawal, preparation, and transfusions follow a careful technique outlined in References 1 and 2. 3. The whole blood, serum, and cells retain the hibernation-inducing power for at least 6 months whether kept at freezer temperature (−15 °C) or liquid nitrogen temperature (−196 °C). 4. The trigger is effective whether used as serum or as dialyzate of that serum (prepared as described). The nondialyzed residue was not effective, and evidence has been found which indicates that an antitrigger may be present in that residue. 5. Cold adaptation may be contraindicated for trigger effectiveness. 6. The titer of trigger in a donor's blood evidently increases as a bout of hibernation lengthens. This is noted by the fact that trigger taken from a donor long in hibernation induces hibernation more rapidly in recipients than does trigger from a donor in a short bout of hibernation. 7. Trigger manifests its effect in winter whether a recipient animal is placed in a colddark or a warm window-lit room. (Trigger effect in a warm window-lit room in a nonhibernating season has not as yet been studied.) 8. Trigger has not been found either in the blood of active or of aroused animals. Thus, effective material is not circumscribed by the expression “winter blood,” but rather by the expression “hibernation blood.” 9. Female animals in all cases are more effective recipients than males, whereas neither sex is a better donor. 10. Recipient animals receiving a trigger and maintained in cold-dark rooms will not show seasonal reversal, rather, have been observed to show bouts of hibernation intermittently for as long as 2 years. They seemingly do not return to the active state. A theoretical approach to hibernation induction is advanced which holds that the trigger is a small molecular material (SM) found in blood taken in hibernation. It is excreted, complexed, and/or metabolized in the arousing process. It may complex with another blood-borne trigger-inhibitor (LM) to form a complex (CM). The entire circannual cycle of hibernation can be related to relative concentrations of SM, LM, and CM. Speculation is further set forth as to hibernation of tissue as contrasted to hibernation of animals. This notion was presaged by others, notably by Lyman, Kayser, and Suomalainen. As Lyman stated (7) “… entrance into hibernation is more than the abandonment of the warm-blooded state.”