Part I
In studying the effect of electronarcosis on thesecretory activity of the pituitary gland, electronarcosishas been applied to guinea pigs and dogs.
Increased secretion of the thyrotropic, adrenocorticotropicand gonadotropic hormones has been shown to resultfrom this passage of electric current through the head ofthe animal. These increases have been shown to be reversibleupon discontinuing the electronarcosis series.
The "tropic" activity following electronarcosis hasbeen shown to be endocrine in nature by demonstrating that indogs the blood serum shows a marked increase in its abilityto produce hypertrophy in the thyroids, adrenals, and testesof day-old chicks.
In guinea pigs a marked elevation of the basalmetabolic rate occurs, subsequent to electronarcosis. In viewof the short latency of this response it has been suggestedthat the increased B.M.R. results from an increased productionof a substance such as the specific metabolic principledescribed by O'Donovan and Collip.
The symptoms observed during electronarcosis inguinea pigs have been described.
Part II
The musculature of the legs of spiders of severalspecies has been studied. For the most part the work ofPetrunkevitch has been confirmed by anatomical observationand physiological experimentation; however, one and possiblytwo heretofore undescribed muscles are reported. The functionof these muscles has not been demonstrated physiologically,but from their structural arrangement they may have a rolein raising the chitinous horseshoe-shaped plate in the femoro-patellarand tibia-metatarsal joints respectively.
An histological study of the leg muscles in spidershas shown them to consist of long, striated, multinucleatefibers loosely associated in parallel groups to form therespective muscles; that is to say, the fibers run parallelfrom origin to insertion for the full length of the muscle.
Distribution of the arterial supply in the legs hasbeen found to be quite extensive. Branching and re-branchingof the main artery results in an elaborate arborizationintimately distributed throughout the muscles.
A discuss ion is presented which indicates that inthose joints which characteristically lack extensor musclesextension is carried out by means of an hydraulic mechanism.Two possible mechanisms are suggested; the one consideredmost probable involves partially closing off the mainarterial stem, thereby diverting a greater amount of bloodinto the membranous pocket formed by the thin flexibleinterarticular membrane of the ventral surface of the joint.Extension is thus a purely mechanical result of the pressureexerted by the balooning-out of the membrane.
Part III
The effectiveness with which different contractions in a number of musclescan be inhibited was investigated. As a measure of this effectiveness the frequencyof inhibition which can just inhibit a contraction with a given frequency of excitationwas determined. It was found that in all system the ratio (Rc) of such inhibitoryfrequencies to that of the excitatory frequencies they can suppress was constantfor a wide range of frequencies.
At high frequencies either the inhibition or the excitation may become lesseffective. This is explained by failure of the respective system to function normallyat such a frequency.
The effectiveness of inhibition of different systems was determined. Somesystems 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 preparationat different times.
Rc values have been found to vary widely. For instance, in the bender inhibitor slowbender system of Paehygrapsus three excitatory impulses are suppressed byone inhibitory impulse; in the closer inhibitor-slow closer system of Cambarusone excitatory impulse needs five inhibitory impulses to counteract its effect. Thefast closer contraction of Cambarus and the fast closer and fast bender contractionof Paehygrapsus were found to be uninhibitable; i.e. no effect of inhibition whatsoeverwas noticed on any of these contractions. All three systems are distinguishedby giving a mechanical response to a single stimulus in contrast with all theinhibitable systems which do not respond to single impulses.
Reduction of the action potentials during inhibition is obtainable in only a fewsystems, namely, the opener inhibitor-opener and the stretcher inhibitor-stretchersystems 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 reductionof the muscle action potential is obtained.
