Svihla1 and his associates of the Department of Zoology, University of Washington, Seattle, noted that, with a 23-gage hypodermic needle, heart blood can be safely drawn from active ground squirrels but that the same technique is usually fatal with dormant (estivating) squirrels. Necropsies showed that death was due to internal hemorrhages. These squirrels thus acted as if they were suffering from a clotting deficiency of the blood.
Studies of blood clotting were therefore made on active and dormant squirrels. By Howell's technique it was found that on an average the blood of nondormant squirrels coagulates firmly in about eight minutes. The blood of a dormant squirrel requires on an average 49 minutes to form a partial clot, a firm clot never forming.
Svihla believes that this prolongation of blood-clotting time is a purposeful adaptation for the dormant state. During this period the heart beats very slowly, with a marked
PROLONGED CLOTTING TIME IN HIBERNATION. JAMA. 1951;147(18):1766. doi:10.1001/jama.1951.03670350046016