NATURE 



409 



THURSDAY, AUGUST 30, 1900. 



RIGHT- AND LEFT-HANDEDNE5iS. 

 Rechts- tind Linkshdndigkeit. Von Dr. Fritz Lueddeckens. 



Pp. vi + 82. (Leipzig : Engelmann, 1900.) 

 "T^HE chief interest of the treatise under consideration 

 J- consists in the exposition of a variety of condi- 

 tions which, in the author's opinion, are associated 

 with that commonly known as right-handedness, a 

 condition which is generally assumed to refer to a 

 greater physical development and functional employment 

 of that side of the body. Moreover, the author seeks to 

 refer all the phenomena upon which his extended con- 

 ception of right- (or left-) handedness is based to a 

 common cause, which he finds in the existence of a 

 higher degree of blood-pressure in the vessels of one 

 side of the head (and in the common mstance, viz. the 

 right-handed one, in the vessels of the left side) than in 

 those of the other. Dr. Lueddeckens is thus firstly con- 

 cerned to prove the existence of such an inequality in 

 blood-pressure as has just been mentioned, and the 

 earlier pages of his book are devoted to this part of the 

 subject. From an account of the embryological history 

 of the arterial system, and the departures from original 

 bilateral symmetry which that system presents, we are 

 led (p. 8) to a study of the hydrodynamic conditions 

 obtaining in the aortic arch in the living subject, and in 

 this connection it is argued that the circumstances are 

 such as will produce a higher blood-pressure in the 

 left than in the right common carotid artery. The 

 greater frequencies of cerebral hyemorrhage, and of 

 embolism of the arteria centralis retince on the left 

 side of the brain, are urged in further support of this 

 view. 



If it be conceded that the cerebral hemispheres may 

 differ in respect of the pressure in their arterial systems, 

 it becomes possible to divide individuals into three classes, 

 viz. those in whom the blood-pressure is higher on the 

 left side ; those in whom the pressure is higher on the 

 right side ; and, finally, there must be a category in which 

 will be ranged such cases as present a degree of blood- 

 pressure which is the same in each hemisphere. The 

 majority of cases will, it is believed, fall within the first 

 of these divisions, and to such cases (ordinary right- 

 handed persons) our attention is first directed : evidence 

 is drawn from a comparison of the structures supplied by 

 the chief branches of the common carotid arteries of 

 each side, and firstly of the structures in the area supplied 

 by the external carotid artery, including various super- 

 ficial structures and also the ear (internal maxillary 

 artery), and the conclusion is arrived at that there is a 

 predominance in growth and a more easily excitable 

 nervous sensibility (auditory sensations being especially 

 observed) on the left side, such preponderance being 

 directly associated with the higher blood-pressure on 

 that side. 



In the second place, a number of observations on the 

 shape of the eyeball, and on the comparative dimensions 

 <^if the two eyes in the same individual, are discussed. 

 NO. 1609. VOL. 62] 



For it is argued that a difference in blood-pressure will 

 find expression in a difference in the shape of the eyeball 

 on the same side, and that this difference in shape will, 

 in turn, be manifested by differences between the two 

 eyes, in respect of sight. And it is finally submitted that 

 observations on the respective refractive powers in the 

 two eyes of a number of persons examined with regard 

 to this point bear out the conclusion which was thus 

 arrived at on a priori grounds. 



Thirdly, differences in the size of the pupil on the two 

 sides are taken as criteria of differences in blood-pressure, 

 the smaller pupil corresponding to the higher blood-pres- 

 sure, and vice versd. Thus we should, according to the 

 author's argument, expect normally to observe differences 

 in this respect. But inasmuch as such difference between 

 the pupils is, by many authorities, considered to accom- 

 pany pathological conditions only, the author is at con- 

 siderable pains to show that a purely physiological 

 difference in size may exist. And so again, his arguments 

 that the difference in blood-pressure will be manifested 

 by a difference in the pupils, and further that the differ- 

 ence is normally (in right-handed persons, that is) indi- 

 cative of a higher blood-pressure on the left side of the 

 head, are considered to be justified by the number of 

 cases in which the smaller of two " physiologically " 

 unequal pupils was observed in the left eye. 



Turning from the special domain of ophthalmic anatomy 

 and physiology, the relative weights of the cerebral hemi- 

 spheres next claim attention, and Hamarberg's results 

 are quoted as indicative of a slight excess of weight in 

 favour of the left hemisphere. The conformation of the 

 several cortical areas is then described, in allusion to 

 their well-known connection with the voluntary produc- 

 tion of movements (and of speech in particular). Sensory 

 phenomena are next considered, and evidence of a right- 

 sided predominance in nervous excitability is adduced 

 from the results of work by Biervliet (on the muscular 

 sense, taste, hearing, sight) ; and lastly, psychical events 

 are dealt with, though with much brevity owing to the 

 difficulty of obtaining relevant evidence. 



Passing briefly over the category of subjects in whom 

 an equal blood-pressure is presumed to obtain on both 

 sides of the head, the remaining class in which the blood- 

 pressure on the right side of the head exceeds that on 

 the left is dealt with much in the same way, and in 

 nearly as much detail, as the first class ; and with very 

 similar results, muiaiis tnuiandis : in other words, 

 Dr. Lueddeckens finds in the majority of left-handed 

 persons the various sources of evidence which have 

 previously been detailed, and which indicate in the left- 

 handed persons a higher blood-pressure on the right 

 side of the head, just as they indicated this condition 

 on the left side of the head in right-handed persons. 

 Interesting observations on the psychical phenomena 

 of young left-handed individuals are recorded, and in 

 particular their difficulties in learning to write, their 

 tendency to adopt mirror-writing, and the greater fre- 

 quency of impediments to speech among the left- 

 handed may here be noted. Finally, the tendency of 

 the left-handed to lie on the left side during sleep is 

 commented upon. 



The foregoing sketch will, it is thought, render the 



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