So77ie Characters in Human Beings 39 



Negroes with an interesting piebald spotting have been re- 

 ported by Keeler. Individuals with this dominant gene have 

 normal dark pigmentation in the head, back, hands, and feet ex- 

 cept for a white head blaze and a white patch under the chin. 

 Their abdomen, sides, arms, and legs are generally white but are 

 speckled with small patches of normally pigmented skin. The 

 pattern of these individuals is essentially the same as that found 

 in the Dalmatian coach dog, the English rabbit, and Hereford 

 cattle. 



Abnormal conditions of skin texture are known. One of the 

 most striking is ichthyosis vulgaris, in which the skin is covered 

 with small, horny flakes or scales. This condition, the result 

 of a dominant gene, produces the "porcupine men" of the side- 

 show. Cockayne has listed an unusual abnormality, ichthyosis 

 hystri gravior, which occurs only in males. Their entire bodies, 

 except for the face, palms, and soles, are covered with dark brown 

 horny growths which appear after they are two months old. A 

 skin defect that can be quite serious is the inherited absence of 

 sweat glands. Individuals lacking these glands cannot perspire. 

 In warm weather they must go to a cooler region or must remain 

 in water or keep their clothes wet to prevent too great a rise in 

 body temperature. This condition may also affect the skin, 

 nails, teeth, hair, mammary glands, and mucous membranes, and 

 persons with this abnormality may be unable to shed tears. 

 The condition is the result of a recessive gene. 



Genes affecting the hair include a dominant gene that produces 

 a white forelock in otherwise dark hair. It was traced for five 

 successive generations in one family. A curious character, the 

 result of a dominant gene, affects the hair in the front of the 

 head in such a way that it falls out when it has grown to five 

 or six inches. When this hair has fallen out new hair comes in, 

 so that affected individuals always have short hair, or bangs, 

 over their foreheads. Other unusual and inherited hair condi- 

 tions are woolly hair and a condition in which* the embryonic 

 hair continues to grow after birth in such abundance that an 

 individual with this dominant gene can appear in circus side- 

 shows as a "dog-faced" man. 



A number of genes affect the axial skeleton, producing abnor- 

 malities that may often have a very harmful effect. The gene 

 for inherited hollow chest reported by Snyder and Curtis pro- 



