blood steadily falls,[133] because the utilization by the tissues is not compensated for by further supply from the liver. Thus, although there may be doubt that analyses of sugar in the blood flowing into and out from an active muscle during a brief period can be accurate enough to prove a clear difference, the evidence from the experiments above cited shows that when the supply of sugar is limited it disappears to a greater or less degree when passed repeatedly through muscular organs. The argument may be advanced, of course, that the sugar which thus disappears is not directly utilized, but must first be changed to glycogen. There is little basis for this assumption. There is, on the other hand, considerable evidence that increasing the blood sugar does, in fact, directly increase muscular efficiency. Thus Locke[134] proved that if oxygenated salt solution is perfused through the isolated rabbit heart, the beats begin to weaken after one or two hours; but if now 0.1 per cent dextrose is added to the perfusing liquid, the beats at once become markedly stronger and may continue with very slow lessening of strength as long as seven hours. And Schumberg[135] noted that when he performed a large amount of general bodily work (thus using up blood sugar) and then tested flexion of the middle finger in an ergograph, the ability of the muscle was greater if he drank a sugar solution than if he drank an equally sweet solution of “dulcin.” He did not know during the experiment which solution he was drinking. These observations have been confirmed by Prantner and Stowasser, and by Frentzel.[136] In experiments on cats, Lee and Harrold[137] found that when sugar is removed from the animal by means of phlorhizin the _tibialis anticus_ is quickly fatigued; but if, after the phlorhizin treatment, the animal is given an abundance of sugar and then submitted to the test, the muscle shows a much larger capacity for work. All this evidence is, of course, favorable to the view that circulating sugar may be quickly utilized by contracting muscles. From the experimental results presented above it is clear that muscles work preferably by utilizing the energy stored in sugar, that great muscular labor is capable of considerably reducing the quantity of stored glycogen and of circulating sugar, and that under circumstances of a lessened sugar content the increase of blood sugar considerably augments the ability of muscles to continue contracting. The conclusion seems justified, therefore, that the increased blood sugar attendant on the major emotions and pain would be of direct benefit to the organism in the strenuous muscular efforts involved in flight or conflict or struggle to be free. The Utility of Increased Adrenin in the Blood as an Antidote to the Effects of Fatigue