Spread Of Influences Research Articles

Inhibition in the eye of Limulus.

In the compound lateral eye of Limulus each ommatidium functions as a single receptor unit in the discharge of impulses in the optic nerve. Impulses originate in the eccentric cell of each ommatidium and are conducted in its axon, which runs without interruption through an extensive plexus of nerve fibers to become a fiber of the optic nerve. The plexus makes interconnections among the ommatidia, but its exact organization is not understood. The ability of an ommatidium to discharge impulses in the axon of its eccentric cell is reduced by illumination of other ommatidia in its neighborhood: the threshold to light is raised, the number of impulses discharged in response to a suprathreshold flash of light is diminished, and the frequency with which impulses are discharged during steady illumination is decreased. Also, the activity that can be elicited under certain conditions when an ommatidium is in darkness can be inhibited similarly. There is no evidence for the spread of excitatory influences in the eye of Limulus. The inhibitory influence exerted upon an ommatidium that is discharging impulses at a steady rate begins, shortly after the onset of the illumination on neighboring ommatidia, with a sudden deep minimum in the frequency of discharge. After partial recovery, the frequency is maintained at a depressed level until the illumination on the neighboring receptors is turned off, following which there is prompt, though not instantaneous recovery to the original frequency. The inhibition is exerted directly upon the sensitive structure within the ommatidium: it has been observed when the impulses were recorded by a microelectrode thrust into an ommatidium, as well as when they were recorded more proximally in single fibers dissected from the optic nerve. Receptor units of the eye often inhibit one another mutually. This has been observed by recording the activity of two optic nerve fibers simultaneously. The mediation of the inhibitory influence appears to depend upon the integrity of nervous interconnections in the plexus: cutting the lateral connections to an ommatidium abolishes the inhibition exerted upon it. The nature of the influence that is mediated by the plexus and the mechanism whereby it exerts its inhibitory action on the receptor units are not known. The depression of the frequency of the discharge of nerve impulses from an ommatidium increases approximately linearly with the logarithm of the intensity of illumination on receptors in its vicinity. Inhibition of the discharge from an ommatidium is greater the larger the area of the eye illuminated in its vicinity. However, equal increments of area become less effective as the total area is increased. The response of an ommatidium is most effectively inhibited by the illumination of ommatidia that are close to it; the effectiveness diminishes with increasing distance, but may extend for several millimeters. Illumination of a fixed region of the eye at constant intensity produces a depression of the frequency of discharge of impulses from a nearby ommatidium that is approximately constant, irrespective of the level of excitation of the ommatidium. The inhibitory interaction in the eye of Limulus is an integrative process that is important in determining the patterns of nervous activity in the visual system. It is analogous to the inhibitory component of the interaction that takes place in the vertebrate retina. Inhibitory interaction results in the exaggeration of differences in sensory activity from different regions of the eye illuminated at different intensities, thus enhancing visual contrast.

ON A PHYSICAL BASIS FOR NUMERICAL PREDICTION OF LARGE-SCALE MOTIONS IN THE ATMOSPHERE

Abstract The small-scale “noise” disturbances of the atmosphere create difficulties for the numerical integration of the equations of motion. For example, their existence demands that very small time differences be used in the integration of the finite-difference equations. To eliminate the noise, a filtering method is devised which consists essentially in replacing the primitive hydrodynamical equations by combining the geostrophic and hydrostatic equations with the conservation equations for potential temperature and potential vorticity. In this way a single equation in the pressure is obtained for the motion of the large-scale systems. A method is suggested for its numerical integration. The spread of data required for a short-period forecast is discussed in terms of the rate of spread of influences or “signal velocity” in the atmosphere. It is shown that a small disturbance is propagated both horizontally and vertically at a finite rate. Estimates are obtained for the maximum signal-velocity component...

Research Items

HOLY WAYS AND HOLY PLACES.—Prof. H. J. Pleure has published in the Sociological Review—a communication to the Conference on Living Religions, recently held at Wembley, on the origin of sites which are or have been held in special veneration as centres of religious cults. Such centres have to a great extent grown up along routes of trade and intercourse such as can be traced so far back, at least, as the late neolithic and early metal ages. There is evidence for the spread of cultural influences between the Iberian Peninsula, France, western Britain and Ireland, southern Sweden, Denmark, and north-west Germany. The megalithic monuments which mark this spread of culture may well have been stations of men of superior culture to which natives would come to trade, their sanctity continuing down to historic times, as is shown by the records of the early Christian Church. The stations along the route followed by Abram from Haran through Palestine-Shechem, Bethel, Hebron, and Beersheba-gathered traditions of sanctity in course of time. Mecca, a station of sanctity far older than Islam, as is shown by the cult of the Black Stone, is a place of contact on the trade way from Arabia Felix northward. Santiago de Compostella is a focus behind alternative ports going back, directly and indirectly to the earlier stone monuments. Similarly St. Davids in South Wales, Canterbury, and possibly St. Andrews, each acted as a focus for sea routes; while Kief analogously is the culture entry for the land and rivers both from the south, by which Byzantine influence reached Muscovy, and from the west. Jerusalem originally was the fortress controlling the trade routes, whether from Hebron to Bethel and Shechem, to Jericho and across the Jordan, or along the western side of the Dead Sea.

THE INFLUENCE OF SANITATION UPON OBSTETRICAL AND GYNECOLOGICAL SURGERY.

It goes without saying that the age in which we live is one of immense progress. In whichever direction the eye is turned in the scientific field the evidences of an intelligent and untiring labor are presented. Contrast the status of scientific knowledge to-day with that of half a century ago and the immense gain in beneficent information and in useful fact is made apparent. In no department of scientific work is this gain more marked than in the domain of preventive medicine. Not only have the manifold causes of diseases been diligently and assiduously sought for and in numerous instances found, but astonishing progress has been made in the direction of preventing the spread of contagious influences and in modifying the effects of such influences when in actual force. The science of Sanitary Medicine has been revolutionized and reconstructed on a foundation of established principles. To the growth