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

by Erasmus Darwin

Other catenations of motions are gradually acquired by frequent voluntary repetitions; as when we deliberately learn to march, read, fence, or any mechanic art, the motions of many of our muscles become gradually linked together in trains, tribes, or circles of action. Thus when any one at first begins to use the tools in turning wood or metals in a lathe, he wills the motions of his hand or fingers, till at length these actions become so connected with the effect, that he seems only to will the point of the chisel. These are caused by volition, connected by association like those above described, and afterwards become parts of our diurnal trains or circles of action.

[3]. All these catenations of animal motions, are liable to proceed some time after they are excited, unless they are disturbed or impeded by other irritations, sensations, or volitions; and in many instances in spite of our endeavours to stop them; and this property of animal motions is probably the cause of their catenation. Thus when a child revolves some minute on one foot, the spectra of the ambient objects appear to circulate round him some time after he falls upon the ground. Thus the palpitation of the heart continues some time after the object of fear, which occasioned it, is removed. The blush of shame, which is an excess of sensation, and the glow of anger, which is an excess of volition, continue some time, though the affected person finds, that those emotions were caused by mistaken facts, and endeavours to extinguish their appearance. See Sect. [XII. 1. 5].

[4]. When a circle of motions becomes connected, by frequent repetitions as above, we can exert our attention strongly on other objects, and the concatenated circle of motions will nevertheless proceed in due order; as whilst you are thinking on this subject, you use variety of muscles in walking about your parlour, or in sitting at your writing-table.

[5]. Innumerable catenations of motions may proceed at the same time, without incommoding each other. Of these are the motions of the heart and arteries; those of digestion and glandular secretion; of the ideas, or sensual motions; those of progression, and of speaking; the great annual circle of actions so apparent in birds in their times of breeding and moulting; the monthly circles of many female animals; and the diurnal circles of sleeping and waking, of fulness and inanition.

[6]. Some links of successive trains or of synchronous tribes of action may be left out without disjoining the whole. Such are our usual trains of recollection; after having travelled through an entertaining country, and viewed many delightful lawns, rolling rivers, and echoing rocks; in the recollection of our journey we leave out the many districts, that we crossed, which were marked with no peculiar pleasure. Such also are our complex ideas, they are catenated tribes of ideas, which do not perfectly resemble their correspondent perceptions, because some of the parts are omitted.

[7]. If an interrupted circle of actions is not entirely dissevered, it will continue to proceed confusedly, till it comes to the part of the circle, where it was interrupted.

The vital motions in a fever from drunkenness, and in other periodical diseases, are instances of this circumstance. The accidental inebriate does not recover himself perfectly till about the same hour on the succeeding day. The accustomed drunkard is disordered, if he has not his usual potation of fermented liquor. So if a considerable part of a connected tribe of action be disturbed, that whole tribe goes on with confusion, till the part of the tribe affected regains its accustomed catenations. So vertigo produces vomiting, and a great secretion of bile, as in sea-sickness, all these being parts of the tribe of irritative catenations.

[8]. Weaker catenated trains may be dissevered by the sudden exertion of the stronger. When a child first attempts to walk across a room, call to him, and he instantly falls upon the ground. So while I am thinking over the virtues of my friends, if the tea-kettle spurt out some hot water on my stocking; the sudden pain breaks the weaker chain of ideas, and introduces a new group of figures of its own. This circumstance is extended to some unnatural trains of action, which have not been confirmed by long habit; as the hiccough, or an ague-fit, which are frequently curable by surprise. A young lady about eleven years old had for five days had a contraction of one muscle in her fore arm, and another in her arm, which occurred four or five times every minute; the muscles were seen to leap, but without bending the arm. To counteract this new morbid habit, an issue was placed over the convulsed muscle of her arm, and an adhesive plaster wrapped tight like a bandage over the whole fore arm, by which the new motions were immediately destroyed, but the means were continued some weeks to prevent a return.

[9]. If any circle of actions is dissevered, either by omission of some of the links, as in sleep, or by insertion of other links, as in surprise, new catenations take place in a greater or less degree. The last link of the broken chain of actions becomes connected with the new motion which has broken it, or with that which was nearest the link omitted; and these new catenations proceed instead of the old ones. Hence the periodic returns of ague-fits, and the chimeras of our dreams.

[10]. If a train of actions is dissevered, much effort of volition or sensation will prevent its being restored. Thus in the common impediment of speech, when the association of the motions of the muscles of enunciation with the idea of the word to be spoken is disordered, the great voluntary efforts, which distort the countenance, prevent the rejoining of the broken associations. See No. [II. 10]. of this Section. It is thus likewise observable in some inflammations of the bowels, the too strong efforts made by the muscles to carry forwards the offending material fixes it more firmly in its place, and prevents the cure. So in endeavouring to recal to our memory some particular word of a sentence, if we exert ourselves too strongly about it, we are less likely to regain it.