The aim of this article is, first, to summarize the literature of the subject, and second, to give in brief the results of certain experimental studies in the field. In part it is B condensed statement of data published in another connection (7).
I. LITERATURE ON LEFT-HANDEDNESS
Investigations of the general problem of left-handedness have confined themselves largely to four aspects: (1) the prevalence of lefthandedness in normal and sub-normal human beings, and its variation with age, sex, race, etc.; (2) its hereditary nature; (3) its origin and cause, and (4) its relationship to "iiiirror-writing."
1. THE PREVALENCE OF LEFT-HANDEDNESS
According t o Gould (10) 6 per cent of all normal human beings are left-handed. Smith (24) gives the percentage as 5; Lombroso (20) and Jones (12) give it as 4; Ballard (4) states the distribution as 2.7 per cent, while Hyrtl (11) and Baldwin (3) give it as 2 per cent.
It is affirmed by Weber (28), Ballard (4), and Smith (24) and denied by Lonibroso (20) that left-handedness is more frequently found among males than females. Lombroso (ZO), Audenino (l), Lattes (18) and Smith (24) find left-handedness more frequent among delinquents. Lattes (18) also finds the characteristic more frequent among negroes. HrdliEka (10a) found it in 4 per cent of Apache and 3.6 per cent of Pima Indian children and adolescents.
According to these investigations the distribution of left-handedness among the normal population ranges from 2 to G per cent, with 4 per cent as the median. The latter is the more reliable figure, in the writer's opinion, and is confirmed by his own investigations (7).
2. THE INHERITANCE OF LEFT-HANDEDNESS
Wilson (30), Merkel (21), Weber (28), Bardeleben (5) , Jordan (14), and Ramaley (22) affirm the hereditary nature of left-handed-389 'See also his "Experimental Study in Left-handedness," Univ. of Chicago Press, 1918.