246 THE TREND OF THE RACE 



that in some even of these five matings the normal parent had 

 unknown deaf relatives. But if the hearing partner have deaf 

 relatives then the proportion of resulting fraternities containing 

 deaf mutes increases to 35 per cent." 



Huth who has made a very useful compilation of data on the 

 subject has tabulated returns from 52 institutions or observers 

 with percentages of deaf mutes of consanguineous origin varying 

 from o to 34.4, but with a general average of over 5 per cent in 

 33 cases, of 10 per cent or over in 21 cases, and 25 per cent or 

 over in 6 cases. Although the variability of these results was 

 used as an argument against the role of consanguineous marriages 

 per se in the production of deafness, the data show that this defect 

 arises from such marriages in an unusually large number of in- 

 stances. 



The problem of the inheritance of deaf -mutism, like that of the 

 transmission of feeble-mindedness, epilepsy and insanity, is com- 

 plicated by the as yet insufi&ciently known influence of syphilis. 

 Dr. Kerr Love has attempted to separate cases of syphilitic origin 

 by the use of the Wassermann reaction. It is only by eUminating 

 such cases, as well as those caused early in life, that the real mode 

 by which deafness is transmitted can be revealed. 



Where people form inbreeding communities different traits are 

 apt to become prevalent in different localities. According to 

 Davenport, "consanguinity on Martha's Vineyard results in 11 

 per cent deaf mutes and a number of hermaphrodites; in Point 

 Judith in 13 per cent idiocy and 7 per cent insanity; in an island 

 off the Maine Coast the consequence is intellectual dullness; in 

 Block Island loss of fecundity; in some of the 'Banks' off the 

 coast of North Carolina, suspiciousness, and an inability to pass 

 beyond the third or fourth grade of school ; in a peninsula on the 

 east coast of Chesapeake Bay the defect is dwarf ness of stature; 

 in George Island and Abaco (Bahama Islands) it is idiocy and 

 blindness (G. A. Penrose, 1905). There is no one trait that re- 

 sults from the marriage of kin; the result is determined by the 

 specific defect in the germ plasm of the common ancestor." 



Such evils of inbreeding as have been discussed may be re- 



