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The increase in twitch tension which follows a brief tetanus of a muscle has been shown to be associated with a diminution of the demarcation potential of the muscle. A similar increase in twitch tension and a similar reduction in demarcation potential can be produced by arterial injection into a muscle of suitable amounts of potassium chloride (Feng, 1938; Brown & Euler, 1938). The effects were so closely similar indeed, that they suggested that the potentiating action of a tetanus on twitch tension was due to a mobilization of K ions in the muscle.The effect of adrenaline in increasing the twitch tension of a muscle has been shown to be due to a direct action upon the contractile mechanism of the muscle fibre (Brown, Biilbring & Burns, 1948), and recently Goffart & Brown (1947) have shown that the effectiveness of adrenaline on muscle is inversely proportional to the amount of potassium in the fluid bathing an isolated preparation. They pointed out also that fatigue, as such, is not a necessary condition for a clear potentiating action of adrenaline upon the muscle twitch. There are many superficial similarities between the effect of adrenaline and the posttetanic potentiation: they are both effects upon the muscle fibre, their time courses are similar and they both appear to be associated with changes in the K+ of the muscle. It appeared probable therefore, that a study of the effect of adrenaline upon the demarcation potential would be profitable. Adrenaline has been found to produce small but constant changes in it, but in the direction of increase of potential and not, as we had expected, in depolarization. METHODSThe majority of the experiments were made on cats anaesthetized with chloralose, 06 mg./kg.; a few cats were decerebrated under ether. The tibialis muscle was prepared for arterial injection (Brown, 1938) and its nerve supply was severed. For tension recording the limb was held in a myographic stand, sometimes vertically, sometimes horizontally, and the tendon was connected to a flat spring myograph. The electrical records were taken with the limb horizontal and the muscle lying in medicinal liquid paraffin in a bath formed by the skin flaps. We cut the sciatic nerve on one

The night monkey, a tropical monkey, is the only nocturnal simian; its thermoregulation was studied for comparison with other nocturnal or diurnal primates and other tropical mammals. Resting metabolic rate was 2.6 W (closed-circuit method) and 2.8 W (open-circuit method), 24 and 18% below the value predicted from body mass. The thermoneutral zone was very narrow; the lower critical temperature (LCT) was 28 degrees C and the upper critical temperature (UCT) was 30 degrees C. The body temperature (Tb) was at its minimum (38 degrees C) at an ambient temperature (Ta) of 25 degrees C, thus below the LCT. At low Ta, the increase in metabolic rate (MR) was smaller than predicted by the Scholander model, since MR intersected to a Ta 13 degrees C above Tb when extrapolated to MR = 0; this was attributed to a decrease of body surface area by behavior. The thermal conductance at the LCT was low: 2.3 W . m-2 . degrees C-1. Above the UCT, panting was the major avenue of heat loss. The response pattern of nocturnal habits, low resting metabolic rate, low thermal conductance, and panting in the night monkey, unique among simians, is found in many other mammals of tropical and hot desert habitats; it may be considered as an alternative adaptation to the thermal environment.

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