PHYSICAL CHARACTERS IX MAN 141 



in animals is due to hereditary transmission of the 

 disposition to cancer. Infection from certain para- 

 sites may, in addition, act as an external stimulus, 

 comparable with Rontgen rays. 



Probabl}^ in principle the conditions are similar 

 in man. Davenport {191 8) shows that the tendency 

 to neurofibromatosis* behaves as a dominant in 

 heredity, though it sometimes skips a generation. 

 It is a rare condition, being found in onh' one in 

 2,000 cases. Loeb believes that in man probably 

 one or more factors are hereditarily transmitted 

 which determine the intensity of the tendenc}^ to- 

 wards cancer development. In many cases, cross- 

 breeding appears to have equalised this tendency in 

 man. But in stationary or relatively pure popula- 

 tions, as in parts of Norway, there is evidence of 

 marked differences in the tendency to cancer in 

 different strains and races. 



Stammering is due to an unusual excitability or 

 instability of cells in the speech centre of the cerebral 

 cortex. The tendency to stammer is clearly inherited, 

 although it not infrequently skips a generation. 

 Bryant (191 7), who has examined over 20,000 cases 

 in a practice extending over thirty-five years, states 

 that at least half had relatives who had suffered from 

 some nervous speech disorder. The condition begins 

 spontaneously in very young children beginning to 

 speak. A case is cited of stammering occurring in 

 four generations, but no other pedigrees are given. 



The Jewish racialf physiognomy', which has been 



* The formation of numerous tumours from necves, and con- 

 taining connective tissue. 



t It is questionable in how far the Jews can be considered a 

 distinct race. Like most races, they have had a mixed origin, 

 probably from Armenoid and Hamitic stocks, as indicated by the 

 presence of both round heads and long heads among modern 

 Jews. The fair Jews evidently have an admixture of Nordic blood. 

 See also Salaman, Trans. Jewish Hist. Soc. Eng., ix. 163, 1922. 



