. A text-book of animal physiology, with introductory chapters on general biology and a full treatment of reproduction ... Physiology, Comparative. 512 ANIMAL PHYSIOLOGY. or adjacent parts of the brain. 7. Under the effects of certain drugs, as physostigmin, morphia, etc. Dilation {Mydriasis).—1. In darkness. 2. On stimulation of the cervical sympathetic. 3. During asphyxia or dyspnoea. 4. By painful sensations from irritation of peripheral parts. 5. From the action of certain drugs, as atropin, etc. The student may impress most of these facts upon his mind hy making the necessary observations
. A text-book of animal physiology, with introductory chapters on general biology and a full treatment of reproduction ... Physiology, Comparative. 512 ANIMAL PHYSIOLOGY. or adjacent parts of the brain. 7. Under the effects of certain drugs, as physostigmin, morphia, etc. Dilation {Mydriasis).—1. In darkness. 2. On stimulation of the cervical sympathetic. 3. During asphyxia or dyspnoea. 4. By painful sensations from irritation of peripheral parts. 5. From the action of certain drugs, as atropin, etc. The student may impress most of these facts upon his mind hy making the necessary observations, which can be readily done. Pathological.—As showing the importance of such connec- tions, we may instance the fact that, in certain forms of nervous disease (e. g., locomotor ataxia), the pupil contracts when the eye is accommodated to near objects, but not to light (the Argyll-Kobertson pupil). In other cases, owing to brain-dis- ease, the pupils may be constantly dilated or the reverse; or one may be dilated and the other contracted. Optical Imperfections of the Eye. The defects to be noticed now are common to all human and probably to the eyes of all mammals, though in some persons certain of them, as astigmatism, are of so serious a character that they require special remedies. Spherical Aberration.—The nature of this defect may be best learned from an examination of Fig. 414, below. It will be seen that rays of light passing through the lens are brought to. Fio. 414.—Illustrating spherical aberration (after I^e ConteV The best image is formed at S, S, but is not perfectly sharply defined even here. a focus, varying with the point of the lens through which they pass, the focusing power of any ordinary convex Jens being greater toward the circumference. This defect is believed to be corrected in the human eye, at least to some extent, by the following: 1. The iris cuts off the more strongly refracted outer rays. 3. The corneal curvature is rather ellipsoidal, so th
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