Why is a particular child right-handed or left-handed? / by George M. Gould.

  • Gould, George Milbrey, 1848-1922.
Date:
1907
Catalogue details

Licence: In copyright

Credit: Why is a particular child right-handed or left-handed? / by George M. Gould. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    -4 right foot, etc., and especially with language, the crowning achievement of humanization. The centers of right- eyedness, right-handedness, right- footedness, speech and writing (with memory and intellect) must be topo- graphically in the left cerebral hemis- phere to insure speed, accuracy, and co-ordination of united sensation, thought, will, and action. In the left- handed, of course, the same law holds of the right side of the brain. In one or in the other, therefore a little by inheritance, and more by necessity—- but not divided or mixed! That is disease—and the god of evolution is a physiologist, not a pathologist! (He seems to have made some pathologists, but not intentionally; and they are pathological!) The right cerebral mechanism, al- though disused for speech-function and right-hand function for 97 per cent, of all ancestors, and for a spe- cial family group, for untold genera- tions, still retains an equal aotitude and mechanism for function with the left. The peripheral mechanism of left hand, left foot, etc., also retain their co-equal educability and profi- ciency. What varies, and what is the special variant cause beyond the com- plete control of the biologic mechanic, which induces the individual incidence of right-handedness and of left-hand- edness ? It is the eyeball. I have measured 20,000 or 30,000, and no one was per- fect in shape. It is a poor and make- shift mechanism apart from its mor- phology ; but, so difficult, so impossi- ble, is the task of making it mathe- matically perfect in shape, i. e., to one- three-lmndredth of an inch of ametro- pia (and that may be pathologic in re- sultant function) that such perfection of dimensions has been impossible. An approach to that perfection has been attained in the ages, and by means of that most powerful of all the agents, the exclusion of the unfit, the exclu- sion of the ocularly unfit. When the child begins to reach out for and to seize upon objects with its hands, the question arises at once— with which hand? One is usually all that is necessary, and one must be se- lected. . Then begins either the life- long and increasing preference, selec- tion, and selectability of the right, or of the left—or the history and perfect- ing of right-handedness, or of left- handedness. The significant thing is the order in which the peripheral func- tions appear and develop in the child. First of all, long preceding, causing, and governing all others, especially of motion, is Vision. The lesson of em- bryology is illustrated in the baby’s life. When the muscles of the arm and hand are ready for any movement, vision has been long ready to direct it and make it purposive. Then the correlated center for speech-phona- tion is located in the brain-half oppo- site that of the dextral eye in the right- eyed, and vice-versa in the left-eyed. The foot-and-leg correlation is latest and always most imperfect and vari- ant. Many tests may be made of the now well-known fact I have so long urged of the dominance of one eye in vision; of the existence, under certain circumstances, of two images of one object (not strabismic, but normal and necessary) ; and of the psychic ignor- ing of the image of the non-dominant eye. A sheet of paper vertically held before the eye, with the edge against the nose, followed by alternate closure and opening of each eye illustrates ; or the pencil or finger may be held in most any position and the gaze fixed beyond it. Other devices prove that certainty of manual seizure, accuracy of mental re-presentations of spacial, topographic, and stereoscopic relations (with precision, safety, etc., of co-or- dinated actions) depend upon the fre- quent preference of the image of one eye, and the ignoring of that of the other. The right eye and right hand must work together, the right eye usually governing the actions of the right hand; and the same of the sinis- tral organs. If now the right eye is more defec- tive, more ametropic, if its vision is poorer, more difficult, or more pain- ful than that of the left, the left eye must be chosen to govern hand-action,