An elementary treatise on human physiology : on the basis of the Précis élémentaire de physiologie / par F. Magendie.

  • Magendie, François, 1783-1855.
Date:
1844
Catalogue details

Licence: Public Domain Mark

Credit: An elementary treatise on human physiology : on the basis of the Précis élémentaire de physiologie / par F. Magendie. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    Amaurosis generally affects the whole of the retina; occasion- ally, however, it confines itself to one or more parts, and thus produces some remarkable anomalies. Thus blank spots appear in the field of vision: when the paralysis is confined to certain points of the retina, or if considerable portions, say one half, of the membrane be diseased, the individual sees only parts of objects. Amaurosis may arise from the morbid condition of the retina, the trunk of the optic nerve, or a portion of the brain. It not unfre- quently arises in one eye, while the other remains perfect; some- times occurring without pain, or even the consciousness of the individual, a knowledge of its existence being revealed to him, perhaps, in accidentally shutting the well eye to examine an ob- ject with the other. Partial and temporary paralysis, causing indistinctness of vision, musci volitantes, &c, not unfrequently arises from sympathy with the disordered state of the stomach.] CHAPTER IV. OF HEARING. Hearing is the function by which we are made acquainted with the vibratory motions of bodies. Sound is to hearing what light is to vision. Sound is the result of an impression produced upon the ear by the vibratory motion impressed on the particles of bodies, by percussion or any other cause. This word describes also the vibratory motion itself. When the particles of a body have been thus put in motion, they communicate it to the elastic bodies which surround them ; these act again in the same man- ner, and thus the vibratory motion is propagated, oftentimes to a considerable distance. Elastic bodies alone, generally speaking, are capable of producing and propagating sound. For the most part, solid bodies produce it, while the air is often the vehicle which transmits it to our ear. We may consider it according to its intensity, note, and tone. The intensity of sound depends on the extent of the vibrations. The note depends on the number of vibrations in a given time, and is divided into sharp and grave. A grave note arises from few vibrations; in a sharp note 4they are very numerous. The most grave note that the ear can perceive is formed by thirty vibrations in a second ; the most sharp, by twelve thousand. But M. Savart has proved, by a series of experiments and ingenious instruments, that the ear can appreciate sounds when there are 48,000 vibrations in a second.* Between these two extremes are included all appreciable sounds, that is, all sounds of which the * See Annal. de Physiologie et Chimie, Octobre, 1830.