THE EXANTHEMATA 



2267 



Purpura. — Schonlein's purpura, Henoch's purpura, and Werlhof 's 

 purpura are not common in the tropics, though we have seen cases. 

 A symptomatic purpura eruption is occasionally seen in the last 

 stage of kala-azar, in malaria and other maladies. 



THE EXANTHEMATA. 



Smallpox, chicken-pox, and measles are very common in the 

 tropics, though scarlet fever is but rarely met with. 



Smallpox, of which we have already given a description (p. i486), 

 is very common, and often spreads in extensive epidemics, and 

 may present the confluent type and the hsemorrhagic type, which 

 is rare in Europe. In colonies under European rule vaccination 

 is extensively practised. The vaccine does not retain its im- 

 munizing properties for more than a few weeks in the tropics, and 

 hence it is advisable for each colony to be provided with a central 

 vaccine depot where the lymph can be prepared under careful 

 supervision. Owing to the habits of the lower classes and to many 

 of the vaccinators being non-medical men, serious infections with 

 other diseases may occur. 



Measles may be difficult to recognize, as the eruption in dark- 

 skinned races is better felt than seen, but the coryza and other 

 symptoms are generally sufficient to enable a correct diagnosis 

 to be made. 



URTICARIA— LICHEN URTICATUS— PRURIGO. 



Urticarial eruptions are as frequent in the tropics as in temperate 

 zones, though to the new-comer the diagnosis of urticaria in dark- 

 skinned natives is far from easy. Of lichen urticatus we have seen 

 several cases among European and half-caste children, and of 

 urticaria pigmentosa we have seen one case- — a European child. 

 We have observed true prurigo of Hebra in two native girls. 



DERMATITIS VENENATA. 



Several tropical plants and grasses produce substances highly 

 irritating to the skin, but the subject has already been treated in 

 Chapter XCIV., p. 2151. The dermatitis so caused may be urticarial, 

 erythematous, eczematous-like, or bullous, and may extend to large 

 portions of the body. The forms of dermatitis venenata due to 

 animal agents, such as ants, bugs, caterpillars, etc., have been 

 already mentioned in Chapters XIV. and XCVI., p. 2200. 



PARASITIC DISEASES. 



Trichophytoses. — In tropical countries, in addition to the tricho- 

 phj^oses peculiar to the tropical climate, several other forms uf 

 trichophytic affections occur which are clinically identical with 

 those met with in temperate zones, such as tinea circinata, tinea 



