92 HEREDITY AND EUGENICS 



the feet showed absence of certain toes, reduction of 

 certain phalanges, and syndactyly. Such combined 

 abnormalities in a line of descent are not infrequent. 

 Stieve (191 6) describes a case in which the thumbs 

 of both hands have an extra joint. He cites 39 cases 

 from the literature in which there is a supernumerary 

 phalanx on both thumbs, and 16 in which it is on 

 only one. In 33 cases of the former condition, 

 occurring in 10 different families, the condition is 

 known to be inherited, while there is no evidence of 

 its inheritance when it occurs on only one hand. 



Danforth (igiga) describes a condition which he 

 calls brachydactyly in fowls. Such birds differ 

 from the normal in that digit IV, instead of having 

 five phalanges and being longer than digit II, 

 varies from as long as II (not longer) to a toe 

 having only two phalanges and no nail. He treated 

 with alcohol {igigb) fowls which w^ere heterozygous 

 for brachydactyly, Polydactyly (extra toes), and 

 white colour — both males and females, the alcohol 

 being inhaled for short periods. A larger percentage 

 of brachydactylous birds was consistently obtained 

 in the offspring of treated males, indicating that 

 germ cells carrying brachydactyly were more re- 

 sistant than normal germ cells, or possibly (though this 

 seems unlikely) that alcohol damaged the sperma- 

 tozoa so as to produce the defect. This experimental 

 method should be applicable to a variety of cases, 

 and furnish evidence of the relative viability of 

 different types of germinal differences. Ultimately 

 it might lead to a method of selectively eliminating 

 certain undesirable types of germ cells. The studies 

 of Pearl on the eifects of alcohol on pure races of 

 fowls, of Harrison with moths, and some other similar 

 results, indicate that in such cases there is a selective 

 weeding out of weaker germ cells, leaving the stronger 

 to take part in development. 



