Zoonomia; Or, the Laws of Organic Life, Vol. II

by Erasmus Darwin

SPECIES.

[1]. Nictitatio irritativa. Winking of the eyes is performed every minute without our attention, for the purpose of cleaning and moistening the eye-ball; as further spoken of in Class [II. 1. 1. 8]. When the cornea becomes too dry, it becomes at the same time less transparent; which is owing to the pores of it being then too large, so that the particles of light are refracted by the edges of each pore, instead of passing through it; in the same manner as light is refracted by passing near the edge of a knife. When these pores are filled with water, the cornea becomes again transparent. This want of transparency of the cornea is visible sometimes in dying people, owing to their inirritability, and consequent neglect of nictitation.

The increase of transparency by filling the pores with fluid is seen by soaking white paper in oil; which from an opake body becomes very transparent, and accounts for a curious atmospheric phenomenon; when there exists a dry mist in a morning so as to render distant objects less distinct, it is a sign of a dry day; when distant objects are seen very distinct, it is a sign of rain. See Botan. Garden, Part I. add. note xxv. The particles of air are probably larger than those of water, as water will pass through leather and paper, which will confine air; hence when the atmosphere is much deprived of moisture, the pores of the dry air are so large, that the rays of light are refracted by their edges instead of passing through them. But when as much moisture is added as can be perfectly dissolved, the air becomes transparent; and opake again, when a part of this moisture collects into small spherules previous to its precipitation. This also accounts for the want of transparency of the air, which is seen in tremulous motions over corn-fields on hot summer-days, or over brick-kilns, after the flame is extinguished, while the furnace still remains hot.

[2]. Deglutitio irritativa. The deglutition of our saliva is performed frequently without our attention, and is then an irritative action in consequence of the stimulus of it in the mouth. Or perhaps sometimes for the purpose of diffusing a part of it over the dry membranes of the fauces and pharinx; in the same manner as tears are diffused over the cornea of the eye by the act of nictitation to clean or moisten it.

[3]. Respiratio et Tussis irritativæ. In the acts of respiration and of coughing there is an increased motion of the air-cells of the lungs owing to some stimulating cause, as described above in Class [I. 1. 2. 8]. and [I. 1. 3. 4]. and which are frequently performed without our attention or consciousness, and are then irritative actions; and thus differ from those described in Class [II. 1. 1. 2]. and [5]. To these increased actions of the air-cells are superadded those of the intercostal muscles and diaphragm by irritative association. When any unnatural stimulus acts so violently on the organs of respiration as to induce pain, the sensorial power of sensation becomes added to that of irritation, and inflammation of the membranes of them is a general consequence.

[4]. Exclusio bilis. The exclusion of the bile from the gall-bladder, and its derivation into the duodenum, is an irritative action in consequence of the stimulus of the aliment on the extremity of the biliary duct, which terminates in the intestine. The increased secretion of tears is occasioned in a similar manner by any stimulating material in the eyes; which affects the excretory ducts of the lacrymal glands. A pain of the external membrane of the eye sometimes attends any unusual stimulus of it, then the sensorial power of sensation becomes added to that of irritation, and a superficial inflammation is induced.

[5]. Dentitio. Toothing. The pain of toothing often begins much earlier than is suspected; and is liable to produce convulsions; which are sometimes relieved, when the gum swells, and becomes inflamed; at other times a diarrhœa supervenes, which is generally esteemed a favourable circumstance, and seems to prevent the convulsions by supplying another means of relieving the pain of dentition by irritative exertion; and a consequent temporary exhaustion of sensorial power. See Class [I. 1. 2. 5]. Sect. XXXV. 2. 1.

The convulsions from toothing generally commence long before the appearance of the teeth; but as the two middle incisors of the lower jaw generally appear first, and then those of the upper, it is adviseable to lance the gums over these longitudinally in respect to the jaw-bones, and quite down to the periosteum, and through it.

As the convulsions attending the commencement of toothing are not only dangerous to life in their greatest degree, but are liable to induce stupor or insensibility by their continuance even in a less degree, the most efficacious means should be used to cure them.

M. M. Lance the gum of the expected teeth quite through the periosteum longitudinally. Venesection by the lancet or by two or three leeches. One grain of calomel as a purge. Tincture of jalap, five or six drops in water every three hours til it purges, to be repeated daily. After evacuations a small blister on the back or behind the ears. And lastly, two or three drops of laudanum according to the age of the child. Warm bath. See Class [III. 1. 1. 5]. and [6].