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From tlrc Dcpcirt n r o i t of I'Ii!lsio/c)(l!/, rrcStc rii Kcsercc Z'n.icersit!/ Medical School, Cleveland, 0.During the past 3 years researches in this laboratory' have convinced us ( 1 ) that hemorrhage which leads to severe and protracted hypotension leads to an irreversible state from which the animal dies after reinfusion of all the blood withdrawn, ( 2 ) that the csrdioand hemo-dynamic course of events is identical with that observed in other types of shock, and (3) that shock so produced by standardized bleeding eventuates in death within 2-8 hours in 75 to 80% of dogs under morphinebarbital anesthesia or, expressed otherwise, may be said to offer an animal a 20-25F chance of maintaining their arterial pre>sures at reasonably normal levels for 4 to 6 hours.This report concerns itself with the use of the method for comparing the effects of hypoand hyperthermia on total survival time. The method for producing standardized hcmorrhagic shock in dogs anesthetized with morphine and barbital has been described pre-vious1y.l I t consists, briefly, in withdrawing blood rapidly until mean arterial pressure has fallen to 50 mm Hg., in holding it a t thi5 level for 90 minutes by repeated small withdrawals of blood, in subsequently reducing mean arterial pressure to 30 mm Hg. €or 45 minutes. in reinfusing the withdrawn blood (heparinized)S and observing the trend of arterial pressures 4-6 hours thereafter. If the pressure * This investigation was supported by a gr:int from tlie ('1onimon\vcalth Fund. t Condensed suriiinlrry of results p-esrnttvl :IS :I thesis f o r partial fulfillnient of requircmt1nts f:lr the degree of M.S. in the Graduate P c h~o l of Western Reserve Vnircrsity. 1 Werle, J . BI., Cosby, R. S., nnd Wiggers. C. .J., A m .declined to 50 mm Hg. or the animal died, shock had occurred; if the animal maintained normal blood pressures 6 hours or better, a nonshock state was declared to exist. Tn the present experiments the time of survival after reinfusion of blood was chosen as a criterion. Operative procedures were kept at a minimum and consisted only in cannulation of the femoral arteries for bleeding and registration of mean arterial pressures and of a femoral vein for reinfusion.Survival times of hyperthermic animals submi tted to standardized bleeding were available in the case of 1 7 animals previously used by other groups in this laboratory1 during the hot summer months of 1942 when room temperatures ranged from 26 to 33°C and rectal temperatures of the dogs varied from 38.8 to 40.1 C. To these were added 7 more animals studied under similar conditions during hot summer days in 1943. Their rectal temperatures ranged from 38.3 to 41.7"C.For comparison, a series of 20 dogs was submitted to the standardized bleeding while their bodies were cooled in a semi-insulated box a t environmental air temperatures of 15-20" C, and with radiating wall surfaces slightly above that of melting ice. I n a few instances, ice bags were also applied for short intervals of time when it seemed desirable to hasten the red...