122 HEREDITY AND EUGENICS 



They had seven sisters who were normal, from which it 

 would appear that the character was male sex-linked — 

 in other words, recessive or suppressed in the presence 

 of the normal X chromosome in females, and 

 dominant or finding expression in the presence of 

 the Y chromosome in males. 



A less extreme form of the same condition (Martin, 

 1818) was Jane Holden, aged three, whose whole skin 

 except the face w^as " covered with small scales, or 

 rather warty or bristle-like projections," light brown 

 to black in colour and constantly exfoliated. The 

 condition began at the age of three months. Her 

 mother was the same, except that the neck, breast, 

 and forearms, as well as the soles of the feet, were 

 free from this condition. Her parents were healthy, 

 and she was the only one of six children having the 

 disease. In this family, unlike the previous ones, 

 the condition is therefore not male sex-linked. 



Still less severe forms of ichthyosis were formerly 

 said to be rather frequent on the Continent, and were 

 called "pellagra." Sedgwick (1861) quotes Itahan 

 statistics among the peasants of Lombardy, in which, 

 in 184 families, there were 671 healthy individuals 

 and 648 showing pellagra. From this it would appear 

 that the condition perhaps involved a simple Men- 

 delian recessive character. In modern studies of 

 pellagra (see Davenport, 191 6) in Italy, the United 

 States, and elsewhere the essential symptoms appear 

 to be inflammation and ulcerations of certain areas 

 (often symmetrically placed) of the skin, often accom- 

 panied by diarrhoea from ulcerations of the intestine. 

 These symptoms are due to the presence of a toxic 

 agent, which may also induce nervous and mental 

 disturbances in some individuals. Variations in 

 these symptoms are partly due to differences in the 

 hereditary constitution of affected individuals, leading 

 to differences in the susceptibility or resistance of 



