100 STUDIES, SCIENTIFIC AND SOCIAL chap. 



between the climate and the diseases of the tropics. Most 

 people form their opinions from the effects of those 

 tropical diseases which prevail in the cities and towns 

 where Europeans most congregate, or of the climate in 

 the very worst portions of the tropical regions. The great 

 trading centres of tropical America, from Havana and 

 Vera Cruz to Rio de Janeiro, owe their extreme unhealth- 

 iness to two main causes — the absence of all effective 

 sanitary arrangements among the native population, and 

 the fact that they were for several centuries emporiums of 

 the slave trade. It is to this latter cause that Dr. C. 

 Creighton, one of the greatest authorities on the history of 

 epidemic diseases, traces the origin and persistence of the 

 fatal yellow fever, which is only endemic in the slave trade 

 area on the two sides of the Atlantic. The slave ships 

 reached their destination in a state of indescribable filth, 

 which year after year was poured out into the shallow water 

 of the harbours, and soon formed a permanent constituent of 

 the soil between high and low water marks. In the East 

 there were no such slave ships and there is no yellow 

 fever ; but the overcrowding in all centres of population, 

 and the neglect of sanitation, both by the natives and by 

 their English rulers in India, who, knowing better, are 

 most to blame, produces and propagates plague and other 

 zymotic diseases. But these are in no way due to the 

 tropical climate, since three centuries ago plague was as 

 prevalent in the cities of England as it is now in those of 

 India. 



Still more commonly associated with the tropics are the 

 various forms of malarial fevers, but these also are in no 

 sense due to the climate, but simply to ignorant dealing 

 with the soil. My own experience has shown me that 

 swamps and marshes near the equator are perfectly 

 healthy so long as they are left nearly in a state of nature 

 —that is, covered with a dense forest or other vegetation. 

 It is when extensive marshy areas are cleared for culti- 

 vation, and for half the year are dried up by the tropical 

 sun, that they become deadly. I have lived for months 

 together in or close to tropical swamps, both in the 

 Amazon valley, in Borneo and in the Moluccas, without a 



