CHAPTER XCIX 



COSMOPOLITAN SKIN DISEASES " 



General remarks — Pyogenic infections — The erythemata — The exanthemata 

 — Urticaria — Dermatitis venenata — Parasitic diseases — Bullous eruptions 

 — Herpes — Eczema, psoriasis, seborrhoea, and dermatitis exfoliativa — 

 Acne — Hyperidrosis and bromidrosis— Lichen — Tumours — Tuberculosis 

 — Syphilis — Ichthyosis — Kaposi's disease — Chloasma — Diseases of the 

 hair and nails — Some cosmopolitan diseases of mucous membranes. 



GENERAL REMARKS. 



In our experience, all the skin diseases met with in temperate zones 

 are also found in the tropics, except those due to intense cold, such 

 as erythema pernio and frost-bite, and even these may also be 

 found in the high mountainous regions of the tropics. 



The diagnosis of some of the cosmopolitan dermatoses may, owing 

 to the colour of the skin of native races, be very difficult to the 

 medical man newly arrived in the tropics. This is probably the 

 cause of some of the statements that such common diseases as lichen 

 planus and psoriasis are absent. There is no doubt, however, that 

 some dermatoses which are frequently met with in temperate zones 

 are less common in the tropics. 



It is stated by some authorities that coloured races are, on the 

 whole, less liable to skin diseases than the white races, but the 

 reverse is more in accordance with our experience. 



A few remarks as to the normal skin of native races may be 

 useful before proceeding to review the various cosmopolitan diseases. 

 In the African races and American negroes who descend from 

 African negro stock (Guinea negroes, Yoloffs, Caffres) the whole 

 skin, especially the derma, is thicker than in the white races. In 

 Indian races the skin is about the same thickness as in Europeans, 

 except in the Tamils, whose skin is somewhat thicker. As noted by 

 Howard Fox, the glandular system — sweat glands and sebaceous 

 glands — -is much more highly developed in the native races, espe- 

 cially the African negroes. The sebaceous secretion is the cause of 

 their peculiar odour and the shining appearance of the skin, and 

 the large secretion of sweat, which, owing to the high temperature, 

 quickly evaporates, is the probable cause of the skin feeling cooler 

 when touched. In native races the hairy system is less developed, 

 except on the scalp; in the African races the hair of the head is 

 generally curly or woolly; in Indian races it is usually smooth. 



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