312 UNIVERSITY OF VIRGINIA PUBLICATIONS 



but a Mendelian interpretation apparently demands the assumption of 

 degrees of dominance; which assumption necessarily involves the recogni- 

 tion of a multiplicity of factors. 



It is interesting to note that all of the affected families lived on the 

 same farm, the normal families having moved to other regions. The family 

 tradition attributes the cancer to the limestone water of the old farm. "We 

 see at once, however, why one of the fourth generation fraternities was 

 wholly normal : its immediate ancestry possessed a germ-plasm from which 

 the cancer-causing factor was eliminated. The other normal fraternity 

 ■of the third generation offers some difficulties; the most plausible inter- 

 pretation which suggests itself rests on the assumption of a reversal of 

 dominance. Of further interest is the fact that males and females appear 

 equally vulnerable to the etiologic factor. The specificity of the heredity 

 of the carcinoma is also significant. 



D-pO 

 dVrO 



[TOM* 



Fig. 41 Neuhofibhoma. 



Further inquiry revealed the fact that A's first mfe was his first cousin 

 (a daughter of his paternal uncle) . This may explain the greater incidence 

 of carcinoma in the childship of this mating; and suggests grave dangers 

 in human close-breeding. 



A second case (fig. 41) is a two-generation history of neuro-fibroma — 

 a comparatively rare tumor condition. An affected father (colored) — 

 the only affected member of his family — had three normal male and two 

 abnormal female children. Here again the abnormality appears partially 

 dominant over the normal. 



While the etiology of cancer remains obscure, it is fruitless to speculate 

 further. The indisputable fact remains however, I believe, that the con- 

 stitutional basis of cancer is as simply hereditary- as other better under- 

 stood human pathologic characters. 



