Abstract: The initial phase of ventricular systole has been termed the phase of isometric contraction because all the cardiac valves are closed while the pressure is rapidly elevated. Cyclic changes in the dimensions of the left ventricle, recorded by gauges applied directly to the ventricular walls have consistently exhibited an abrupt expansion of the internal diameter, external circumference and external length of the chamber at the onset of systole. Apparently the longitudinal axis of the chamber is abruptly shortened by early contraction of papillary muscles and trabeculae carnae. The lateral walls bulge outward so that the chamber assumes a more spherical configuration as the internal pressure rises. It is doubtful that any of the myocardial fibers actually contract without a change in length, and the term "isometric contraction" is not appropriate for this phase. The initial stage of ventricular systole is actually a period of asynchronous contraction or sphericalization.

Abstract: T HIS an REPORT presents the first results investigation into the effects of of 1. population size on the adrenal glands, and on the reproductive function of mammals. The present study is restricted to mice in confined populations of fixed sizes. This study was prompted by the suggestion that stress was produced in the individuals of a mammalian population in proportion to the population density (I). The hierarchical social organization present in most mammalian populations should contain the necessary elements to produce a density-dependent stress reaction (2, 3). Changes in population density theoretically should produce proportional changes in the size of the adrenal gland, primarily of the cortex. Also one would predict changes in the reproductive organs in opposition to the changes in the adrenal glands (4). Such a density-dependent physiological mechanism operative in the individuals of a population would govern population growth. This mechanism would also aid in explaining the marked susceptibility of high density populations to epidemic diseases, environmental hardships, or idiopathic shock disease (s), depending on dose-time relationships (6) I

Abstract: ANY electrophysiological experiments M have been made in order to determine the properties of the chemoreceptors of the tongue of the rat (I). Comparison of some of the results with those attained by investigators using other techniques revealed differences in the response to a series of inorganic salts among animals belonging to various phylogenetic orders. For example, the behavioral data obtained with human subjects does not correlate directly with the electrophysiological data obtained on rats. Such differences could be explained in either of two ways. First, the behavioral data represents a complex response of the over-all animal to the stimulation of the tongue. This involves many complex processes other than those present in the response of a particular group of chemoreceptors as recorded electrophysiologically. Second, actual differences in the response of the chemoreceptors on the tongue may be present from one species of animals to another. The latter possibility was previously suggested as a consequence of a theoretical treatment of the mechanisms involved in the stimulation of taste receptors by salts (2). It has been found that the ions are very weakly bound to the receptors. Therefore, the binding of various salts should be dependent upon the over-all configurations of the receptor molecules, the available side chains, the proximity of neighboring molecules, etc. It is to be expected that these differences should be accentuated from one species to another. It is the purpose of this paper to show that differences in respon stimu lus do occur from one .se to species a chemical to another.

Abstract: THE PEAK VALUE of the action potential of the vertebrate myelinated fiber has been previously recorded by a number of investigators. (1-5 and others). Values range from about 60-155 mv depending on the method employed. These methods may be divided into three general categories. The action potential at the node of a single fiber may be estimated from a knowledge of the action current in the axis-cylinder and the resistances in the various parts of the nerve fiber. Action currents have been determined by measuring the potential drop across a low resistance shunting the isolated section of a nerve fiber (2) and the resistances involved have been measured to a first approximation (cf. also 6, p. 32), but the uncertainty in the latter measurements lends considerablelimitation to the accuracy of the action potential estimated by this method. A second method adopted by Huxley and Stgmpfli measures the peak value of the action potential by determining the amplitude of a rectangular voltage pulse just necessary to buck out the action potential of the fiber. The method suffers from errors introduced by the capacitative flow of current across the myelin sheath (see e.g. 6, fig. 33). The third method measures the action potential of a single fiber by introducing a hyperfine glass pipette electrode into the fiber (4, 5). Errors due to capacitative losses between the fluid inside the microelectrode and the external solution are probably adequately compensated for by the use of capacitative positive feedback in the amplifier (7-9). However, after the microelectrode is introduced into the fiber there occurs an apparent prolongation of the time required for the impulse to jump across the internode impaled and a rapid deterioration of action potential suggesting damage to the fiber. Thus, the action potential recorded by this method is also subject to some doubt. Most of these difficulties are avoided by connecting the isolated single fiber directly to the grid of a high impedance amplifier developed for use with microelectrodes.Capacitative effects can be minimized by exposing the isolated internode to dry air and by utilizing a positive feed-back in the amplifier. Injury effects are avoided by using the fiber internode itself as a micro-electrode extension connecting the amplifier grid to the inside of the active node.