HEREDITARY TYPE OF CHARACTER STUDIED. 47 



(figs. 4, 7, 11, and 18). The shortening of the affected phalanx is here 

 so pronounced that an external examination might lead to the con- 

 clusion that it was entirely absent. On the other side, we have cases 

 where heterozygous individuals show so slight an alteration that the 

 affected individuals themselves do not realize that they are brachy- 

 phalangous. This is the case in most of the individuals who show the 

 B-type of brachyphakngy. 



The most instructive example here is the individual 1151.2 9 S. G. 

 (figs. 13 and 14). Even measurements provided by the radiographs 

 of her hands fall within the limits of extreme variation in a correlation 

 table made up from measurements from normal hands (p. 53). The 

 slight shortening of the distance between the second and third grooves 

 of the indices is as a diagnostic very uncertain, and from the examina- 

 tion of her hands it would be perfectly allowable to conclude that she 

 is somatically normal. That she nevertheless is genetically brachy- 

 phalangous is shown by the fact that her son is brachyphalangous of 

 the B !-type. 



This controlled case is perhaps the first in human material where 

 an individual heterozygous for a dominant gene is shown to be somati- 

 cally normal. It is valuable because an exact examination can be 

 carried out through the radiograph, while the test of the genetic con- 

 stitution at the same time is at hand. The importance of such an 

 analyzed case is obvious from several points of view: In the first 

 place it gives a satisfactory explanation of many contradictions in 

 records concerning heredity in man. The situation often met with in 

 such publications, that characters which in some generations show a 

 clear Mendelian inheritance are recorded as behaving in a way dis- 

 agreeing with Mendel's laws, is easily explained by the supposition of 

 a similar occurrence. Cases are well known where authors have con- 

 cluded from such material that the results obtained in experimental 

 heredity work in animals and plants can not be applied to inheritance 

 in man. 



A very characteristic example of this type is Rabaud's paper as 

 recently as 1912. In his severe criticism of "Le dogme mendelien" 

 as applied to human heredity he arrives at the following conclusion : 



"Un jour viendra peut-etre ou, grace a lui [i. e., 'le langage physico-chi- 

 mique '] les phenomenes de la vie, les phenomenes he'reditaires en particulier, 

 pouront etre soumis au calcul. Ce jour-la, n'en doutons pas, les formules 

 mendelien paraitront a nos arriere-neveux prodigieusement naiives." 



This criticism is mainly based on an analysis of material collected 

 by Vidal (10), who followed a case of hereditary brachyphalangy 

 through four generations "sans se preoccuper en aucune fagon du 

 point de vue mendelien" (Rabaud). 



It is true that the pedigree given by Vidal shows exceptions from 

 the Mendelian rule that a dominant character never skips a generation, 



