[96] Those desirous of further information on the subject than that contained in this work, are referred to Mitchell’s ‘Manual of Assaying,’ and to the various memoirs of Gay-Lussac, Chaudet, D’Arcet, Tillet, Brande, Ure, Henry, and others.
Assay of the Touch. The fineness of JEWELRY, and of small quantities of GOLD which it is either impossible or inconvenient to assay according to the usual method, is generally determined by means of touch-needles and touch-stones. The former are made in sets, containing gold of different degrees of fineness, and differently alloyed with copper and silver. The latter are usually of black basalt; but pieces of good black pottery answer the purpose very well. The mode of using them is to mark the stone with the sample under examination, and to compare its appearance, hardness, colour, &c., with that produced by one or more of the needles. When the two are similar, the quality or ‘fineness’ is considered to be the same. The marks are then further examined by heating the ‘touch-stone’ to redness, and moistening the strokes with aquafortis, when the appearance resulting from oxidation, &c., differ according to the nature and quantity of the alloy. A nearly similar method is sometimes adopted with SILVER; but the characteristics are scarcely so distinct with the metal. (See above.)
Hu′mid Assaying, Humid Assay. Terms applied to the estimation of the quantity of gold and silver in ores and alloys in the moist way, more especially by the method known as volumetrical analysis. See Gold (Estim.), Silver (Estim.), Volumetrical Analysis, &c.
ASSIMILA′TION. [Eng. Fr.] Syn. Assimila′tio, L.; Aneigung, Verähnlichung, &c., Ger. In physiology, the conversion of food into nutriment, and finally into the substances which compose the bodies of animals and plants; the function of nutrition.
ASTHEN′IC. Syn. Asthen′icus, L.; Asthénique, Débile, Fr.; Schwach, Ger. Weak; debilitated. In pathology, an epithet of diseases (ASTHEN′IC DISEASES) accompanied by great and well-marked debility.
ASTHEN′OPY. Syn. Astheno′pia, L. In pathology, incapacity to keep the eyes fixed on near or small objects for any length of time without confusion of vision. The common causes are over-exertion of the eyes, particularly by artificial light, or by a very brilliant one, or during convalescence; congestion of the ocular vessels; debilitating discharges or indulgences; and general nervous debility, however produced. It “appears to consist in weakness of the apparatus by which the eye is adjusted for the vision of near objects;” and
along with this “there is an irritable state of the retina, connected in some manner with a tendency to internal congestion of the eyes.”[97] The treatment may consist of rest to the eyes, and ablution of them in cold water, with such other efforts to restore their tone and the general health as are noticed under Amaurosis. The prospect of complete cure, when the cause is not removable, is unfavorable; but even when confirmed the disease is not likely to end in blindness. The use of convex spectacles of very low power will generally be found serviceable. See Eye, Spectacles, Vision, &c.
[97] T. W. Jones, ‘Defects of Sight,’ Lond., 1856; p. 82.
ASTH′MA (ăst′mă[98]). [Eng., Ger., L., Gr.] Syn. Asthme, Fr.; Engbrüstigkeit, Ger. In pathology, a well-known disease coming on by fits, and characterised by shortness and difficulty of breathing, accompanied by a wheezing sound, cough, stricture and tightness of the chest, with other like symptoms. These gradually increase until the patient can no longer remain in a recumbent position, being, as it were, threatened with immediate suffocation; and they generally terminate, after the lapse of a few hours, in copious expectoration. The attack usually commences towards evening, and the symptoms increase in urgency during the night—often occurring suddenly after the first sleep—until at length, on the approach of morning, a remission takes place, and, in all probability, the patient, worn out and exhausted, falls into a sound sleep. On awaking in the morning he still feels the ‘tightness’ at the chest, breathes with some difficulty, which is increased by moving, and cannot lie in bed unless his head and shoulders are greatly raised. After a repetition of the fits for some nights, they at length moderate, and after more considerable remissions, pass off at last, leaving the patient in his usual state of health for a time, or until fresh exciting causes produce a return of the disease. For an evening or two previous to the fit the patient generally feels drowsy, indolent, and low-spirited, and experiences a sensation of fulness about the stomach, with headache, general uneasiness, and indigestion—these are the premonitory symptoms.
[98] Asth′ma (with th fully sounded), as given by Knowles, is difficultly pronounceable, and is now obsolete.