. Elements of human physiology. Physiology. 578 PHYSIOLOGY vagus is also exactly analogous to a successive contrast effect. During stimulation of the vagus the breaking down of the contractile substance is stopped or checked, so that building up or anabolism can go on without interruption. When the excitation of the vagus ceases there is an extra store of contractile material in the muscle-cells. This causes the beat to be more vigorous, and we may say that the increased anabolism has been followed by a period of in- creased katabolism, just as strong stimulation of a part of the retina with g
. Elements of human physiology. Physiology. 578 PHYSIOLOGY vagus is also exactly analogous to a successive contrast effect. During stimulation of the vagus the breaking down of the contractile substance is stopped or checked, so that building up or anabolism can go on without interruption. When the excitation of the vagus ceases there is an extra store of contractile material in the muscle-cells. This causes the beat to be more vigorous, and we may say that the increased anabolism has been followed by a period of in- creased katabolism, just as strong stimulation of a part of the retina with green (anabolism) gives rise to a red after- image (katabolism). Visual Judgments Size.—The apparent size of an object is determined by the magnitude of its image formed on the retina. As will be evident from the diagram (Fig. 263), the apparent size in any diameter of any given object is inversely proportional to the distance. Thus the size of the image on the retina of an object two inches long at a distance of one foot is equal to the image of an object four inches long at a distance of two feet. Fig. An object can be seen if the visual angle subtended by it (the angle A c B in Fig. 263) is not less than sixty seconds. This is equivalent to an image on the fovea cen- tralis of the retina about 4 /x ^ across, which corresponds to the diameter of a cone. Estimation of distance depends partly on muscular sensa- tions from the degree of accommodation and of convergence of the optic axes, partly on comparisons of the apparent size of the object with that of a neighbouring object (such as a man) the real size of which is known, and partly on fx = 0-001 Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Starling, Ernest Henry, 1866-1927. Chicago : W. T. Keener
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