I. The Effect of Electronarcosis on the Secretory Activity of the Pituitary Gland. II. Studies on the Extensor Mechanism of the Spider Leg. III. A Comparative Study of Peripheral Inhibition in Decapod Crustaceans

Abstract

Part I In studying the effect of electronarcosis on the secretory activity of the pituitary gland, electronarcosis has been applied to guinea pigs and dogs. Increased secretion of the thyrotropic, adrenocorticotropic and gonadotropic hormones has been shown to result from this passage of electric current through the head of the animal. These increases have been shown to be reversible upon discontinuing the electronarcosis series. The tropic activity following electronarcosis has been shown to be endocrine in nature by demonstrating that in dogs the blood serum shows a marked increase in its ability to produce hypertrophy in the thyroids, adrenals, and testes of day-old chicks. In guinea pigs a marked elevation of the basal metabolic rate occurs, subsequent to electronarcosis. In view of the short latency of this response it has been suggested that the increased B.M.R. results from an increased production of a substance such as the specific metabolic principle described by O'Donovan and Collip. The symptoms observed during electronarcosis in guinea pigs have been described. Part II The musculature of the legs of spiders of several species has been studied. For the most part the work of Petrunkevitch has been confirmed by anatomical observation and physiological experimentation; however, one and possibly two heretofore undescribed muscles are reported. The function of these muscles has not been demonstrated physiologically, but from their structural arrangement they may have a role in raising the chitinous horseshoe-shaped plate in the femoro-patellar and tibia-metatarsal joints respectively. An histological study of the leg muscles in spiders has shown them to consist of long, striated, multinucleate fibers loosely associated in parallel groups to form the respective muscles; that is to say, the fibers run parallel from origin to insertion for the full length of the muscle. Distribution of the arterial supply in the legs has been found to be quite extensive. Branching and re-branching of the main artery results in an elaborate arborization intimately distributed throughout the muscles. A discuss ion is presented which indicates that in those joints which characteristically lack extensor muscles extension is carried out by means of an hydraulic mechanism. Two possible mechanisms are suggested; the one considered most probable involves partially closing off the main arterial stem, thereby diverting a greater amount of blood into the membranous pocket formed by the thin flexible interarticular membrane of the ventral surface of the joint. Extension is thus a purely mechanical result of the pressure exerted by the balooning-out of the membrane. Part III The effectiveness with which different contractions in a number of muscles can be inhibited was investigated. As a measure of this effectiveness the frequency of inhibition which can just inhibit a contraction with a given frequency of excitation was determined. It was found that in all system the ratio (Rc) of such inhibitory frequencies to that of the excitatory frequencies they can suppress was constant for a wide range of frequencies. At high frequencies either the inhibition or the excitation may become less effective. This is explained by failure of the respective system to function normally at such a frequency. The effectiveness of inhibition of different systems was determined. Some systems show a very constant Rc value; in a second group Rc varies within wider limits; and a third group shows two distinct Rc's sometimes in the same preparation at different times. Rc values have been found to vary widely. For instance, in the bender inhibitor slow bender system of Paehygrapsus three excitatory impulses are suppressed by one inhibitory impulse; in the closer inhibitor-slow closer system of Cambarus one excitatory impulse needs five inhibitory impulses to counteract its effect. The fast closer contraction of Cambarus and the fast closer and fast bender contraction of Paehygrapsus were found to be uninhibitable; i.e. no effect of inhibition whatsoever was noticed on any of these contractions. All three systems are distinguished by giving a mechanical response to a single stimulus in contrast with all the inhibitable systems which do not respond to single impulses. Reduction of the action potentials during inhibition is obtainable in only a few systems, namely, the opener inhibitor-opener and the stretcher inhibitor-stretcher systems of Cambarus and the crabs. (In the crabs this applies only to the 'true' inhibitors.) In all other systems, including every system of Panulirus, no reduction of the muscle action potential is obtained.