458 DISEASES OF THE SKIN 



SECTIOxN VI. 



DISEASES OF THE SKIN. 



INTRODUCTION. 



The skin diseases of temperate climates are prevalent in the Tropics 

 with few exceptions, but because of differently coloured skins their 

 diagnosis is often somewhat difficult, and clinical characters alone are 

 insufficient for their discrimination. 



The skins of Tropical races differ from those of temperate climates 

 in thickness, pigmentation, sebum, sweat and hair. 



The skin of the African negro, and to a less extent that of the 

 Indian races, is somewhat thicker than that of the European, thus 

 affording a good protection for his poorly clad body in the rough-and- 

 tumble life he lives. 



The pigmentation is marked and characteristic of tropical natives. 

 It is present at birth, giving the baby a muddy appearance, then 

 darkens rapidly during the first few weeks, and slowly until puberty. 

 Perhaps this is a provision of Providence for protecting them against 

 the sun's rays. 



The sebaceous glands are more highly developed, the secretion 

 giving a more glossy appearance to the skin and a characteristic odour 

 so readily noticed by the new-comer to the Tropics. This excess of 

 sebum is also protective, as fat is a bad conductor of heat. 



The secretion of sweat is also in excess. It evaporates readily and 

 keeps the skin cool. Profuse sweating may also be the result of nerve 

 exhaustion or of a blood toxaemia calling for the elimination of toxins. 



The hair is poorly developed. It is smooth in Indian races and 

 curly in African natives, the woolly nature being due to the spiral hair 

 follicles of the scalp. Hair growths about the face are, as a rule, thin 

 an-d shaggy. The lanugo hair is but poorly developed. 



Pathological conditions of the skin undoubtedly have predisposing 

 factors in the climatic influences of the Tropics. 



A hot dry climate causes rapid evaporation of sweat and a dry 

 *' cracked " skin, easily injured, while a moist heat causes damp 

 sebaceous deposits favourable for the development of skin parasites 

 and a softening of the skin which facilitates disease. 



