August 6, 1909] 



SCIENCE 



183 



found among them. But when a binocular 

 field of regard has developed and objects which 

 are placed directly in front of the animal may 

 be seen, the preferred use, for all dexterous 

 manual acts, of one hand over the other, be- 

 comes a necessity. What is it that determines 

 that the right, rather than the left, hand is, as 

 a matter of fact, preferred by some 94 per cent. 

 of civilized men? 



2. It is the eyeball. I have measured 20,000 or 

 30,000, and no one was perfect in shape. It is a 

 poor and makeshift mechanism even apart from 

 its morphology; ... If now the right eye is the 

 more defective, more ametropic, if its vision is 

 poorer, more difficult, or more painful than that 

 of the left, the left eye must be chosen to govern 

 hand-action, and so, of course, the left hand will 

 become habitually the more chosen, the more ex- 

 pert, and the more educated, for the special task, 

 and soon the child is seen to be left-handed ( p. 58 ) . 



That is to say, the hand on the side of the 

 more perfect eye will be the hand preferred 

 for skillful acts. 



3. The centers of righteyedness, righthanded- 

 ness, rightfootedness, speech and writing (with 

 memory and intellect) must be topographically in 

 the left cerebral hemisphere to insure speed, ac- 

 curacy, and coordination of united sensation, 

 thought, will and action (p. 55). 



Whatever criticism may be passed upon cer- 

 tain aspects of the theory, the dependence of 

 movement upon vision must be accepted as a 

 fact. But, the ultimate reason for this de- 

 pendence must not be lost sight of; the reason, 

 namely, that the contraction of muscles is the 

 final term in the sequence of events called the 

 reflex act, of which the excitement of a sense 

 organ is the first term. Sensation, therefore, 

 in all conscious acts, must precede movement. 

 From this standpoint the relation of vision 

 to movement is not peculiar. The intimate 

 connection between sight and action is due to 

 the high development of the visual organ and 

 the consequent importance of visual percepts 

 in the mental life of the higher animals. But, 

 that the right or left hand should come to be 

 used exclusively for all highly specialized ac- 

 tions, as a consequence of the right or left eye 

 being more nearly emmetropic than the other, 



seems to the reviewer to be untenable for 

 several reasons. (1) In binocular vision it is 

 impossible to distinguish the field of vision of 

 one eye from that of the other. To all intents 

 and piirposes, the two eyes function as one. 

 Even if the right eye, for example, were vastly 

 worse than its mate, the right half of the field 

 of vision would not be less clear than the op- 

 posite half. The whole field would suffer a 

 uniformly distributed defect; but, unless some 

 special test were made, the patient would be 

 entirely ignorant of the fact that his right 

 and not his left, eye was defective. With a 

 uniformly dim, or a uniformly clear, field of 

 vision where is there any motive iii vision to 

 the use of one, rather than the other, side of 

 the body ? (2) If, as the author seems to hold, 

 the field of vision of each eye remains distinct 

 from the other, even in binocular vision, and 

 if each eye retains potential control of the 

 muscles of the corresponding side of the body, 

 it is difficult to see what has been the gain of 

 binocular, over monocular, lateral, vision. 



... it should be remembered that forward move- 

 ment of a four-footed animal, composed of two 

 poorly united or co-ordinated longitudinal halves, 

 must be by means of the governors of all move- 

 ment — vision. One organ of this vision was for 

 the one badly coordinated half-body, the other 

 for the opposite half. The brain was halved, also, 

 but a slow and poor correlating mechanism was 

 begun and is being improved, at present much 

 improved. Kven now the right eye is united in 

 function with the right hand, the right foot, etc., 

 and especially with language, the crowning 

 achievement of humanization (p. 55). 



(3) The author states that the center for 

 " righteyedness " is in the left, and, by impli- 

 cation, the center for " lefteyedness " in the 

 right, hemisphere of the brain. Now, as a 

 matter of neurology, as, no doubt, the author 

 is fully aware, the macular region of each 

 retina is connected with both hemispheres, 

 and it is only the corresponding peripheral 

 regions of the retinas which are exclusively as- 

 sociated with one or the other hemisphere. 

 Suppose, now, that the right eye of an infant 

 of six months were normal and the left eye 

 badly astigmatic. In accordance with our 



