Conceivably the two secretions might act in conjunction, or each might have its own function alone. Thus adrenin might serve in coöperation with nervous excitement to produce increase of blood sugar, or it might have that function and other functions quite apart from that. Before these possibilities are considered, however, the value of the increased blood sugar itself will be discussed. The Utility of the Increased Blood Sugar as a Source of Muscular Energy When we were working on emotional glycosuria a clue to the significance of the increase of sugar in the blood was found in McDougall’s suggestion of a relation between “flight instinct” and “fear emotion,” and “pugnacity instinct” and “anger emotion.” And the point was made that, since the fear emotion and the anger emotion are, in wild life, likely to be followed by activities (running or fighting) which require contraction of great muscular masses in supreme and prolonged struggle, a mobilization of sugar in the blood might be of signal service to the laboring muscles. Pain--and fighting is almost certain to involve pain--would, if possible, call forth even greater muscular effort. “In the agony of pain almost every muscle of the body is brought into strong action,” Darwin[121] wrote, for “great pain urges all animals, and has urged them during endless generations, to make the most violent and diversified efforts to escape from the cause of suffering.”[*] *[Footnote: It is recognized that both pain and the major emotions may have at times depressive rather than stimulating effects. For example, Martin and Lacey have shown (American Journal of Physiology, 1914, xxxiii, p. 212) that such stimuli as would induce pain may cause a fall of blood pressure, and they suggest that the rise of blood pressure commonly reported at times of painful experience is due to the psychic disturbance that is simultaneously aroused. Conceivably there is a relation between recognizing the possibility of escape (with the psychic consequences of that possibility) and the degree of stimulating effect. Thus pains originating from the interior of the body, or from injuries sure to be made more painful by action, would not likely lead to action. On the other hand, the whip and spur illustrate the well-known excitant effect of painful stimuli. Similarly in the case of the strong emotions, the effect may be paralyzing until there is a _definite deed to perform_. Thus terror may be the most depressing of all emotions, but, as Darwin pointed out (_Loc. cit._, p. 81), “a man or animal driven through terror to desperation is endowed with wonderful strength, and is notoriously dangerous in the highest degree.”]