*[Footnote: These earlier investigations, in which an extract of the entire gland was used, made no distinction between the action of the medulla and that of the cortex. It may be that the weakness following removal or disease of the adrenals is due to absence of the cortex (see Hoskins and Wheelon: American Journal of Physiology, 1914, xxxiv, p. 184). Such a possible effect, however, should not be confused with the demonstrable influence of injected adrenin (derived from the adrenal medulla alone) and the similar effects from adrenal secretion caused by splanchnic stimulation.] The foregoing evidence indicates that removal of the adrenals has a debilitating effect on muscular power, and that injection of extracts of the glands has an invigorating effect. It seemed possible, therefore, that increased secretion of the adrenal glands, whether from direct stimulation of the splanchnic nerves or as a reflex result of pain or the major emotions, might act as a dynamogenic factor in the performance of muscular work. With this possibility in mind L. B. Nice and I[75] first concerned ourselves in a research which we conducted in 1912. The general plan of the investigation consisted primarily in observing the effect of stimulating the splanchnic nerves, isolated from the spinal cord, on the contraction of a muscle whose nerve, also isolated from the spinal cord, was rhythmically and uniformly excited with break induction shocks. When a muscle is thus stimulated it at first responds by strong contractions, but as time passes the contractions become weaker, the degree of shortening of the muscle becomes less, and in this state of lessened efficiency it may continue for a long period to do work. The tired muscle which is showing continuously and evenly its inability to respond as it did at first, is said to have reached the “fatigue level.” This level serves as an excellent basis for testing influences that may have a beneficial effect on muscular performance, for the benefit is at once manifested in greater contraction. In the experimental arrangement which we used, only a connection through the circulating blood existed between the splanchnic region and the muscle--all nervous relations were severed. Any change in muscular ability, therefore, occurring when the splanchnic nerve is stimulated, must be due to an alteration in the quantity or quality of the blood supplied to the laboring muscle. Cats were used for most experiments, but results obtained with cats were confirmed on rabbits and dogs. To produce anesthesia in the cats and rabbits, and at the same time to avoid the fluctuating effects of ether, urethane (2 grams per kilo body weight) was given by a stomach tube. The animals were fastened back downward, over an electric warming pad, to an animal holder. Care was taken to maintain the body temperature at its normal level throughout each experiment. The Nerve-muscle Preparation