In a series of experiments on dogs, it was found that core-induced hypothermia of 10° C does cause a decrease in vascular tone. The blood vessels maintain their ability, however, to respond to epinephrine, norepinephrine, acetylcholine, and reflex changes as mediated through the carotid sinus. It was of interest in these studies to note that the response to vagal stimulation was blocked at a somewhat higher temperature than was the response to sympathetic stimulation. However, the dogs still responded to acetylcholine. Due to causes as yet undetermined, muscle blood flow was greatly diminished during core-induced hypothermia. This diminution or shift perhaps augments the flow in the central circuit and may be a protective mechanism. Quinidine does not abolish the temperature gradients in muscle. It did reduce the reactivity of the vascular tree, and perhaps in this manner is helpful in maintaining an adequate perfusion of the vital central areas. Abolition of all vascular control, in spite of the attractiveness of the theory of uniform perfusion, may not be advantageous.