WHITE RACE IN THE TROPICS — WARD 563 



tlie orifjiii and conditions of malarial infection, a close relation 

 between temperature and the occurrence of malaria was observed, so 

 distinct that from then on the line of a mean annual temperature of 

 60° F. hfis l)een considered as markin<j: the polar boundaries of recog- 

 nized malarial infection, ami winter cold has been seen to be the great 

 barrier against the occurrence and spread of the disease. Rainfall 

 is important because the malaria-bearing mosquito passes one stage 

 of its life in water. Hence lakes, and especially marshes, pools, and 

 swamps are critical as breeding places of the mosquitoes. Digging 

 up the soil results in hollows where puddles and pools may collect. 

 In early days, it was believed that stirring up the soil gave rise to 

 certain no.xious exhalations from the ground, and that these vapors 

 or gases produced the disease. It is easy to see how that belief 

 originated, and why it persisted until medical science wholly dis- 

 proved it. 



Tropical dysentery " slays outright, and makes miserable wrecks 

 of white men in the Tropics," as a recent writer has put it, doubtless 

 without exaggeration. Dysentery has its real home in tropical 

 climates, and increases in severity and in frequency with approach to 

 the Equator. Some form of it is always present in low latitudes, 

 and it is there next in importance to malaria in causing high death 

 rates, and in its lasting effects. In contrast with the case of malaria 

 and of yellow fever, altitude can not be relied on to give relief. 

 Residents on mountains sometimes suffer more than do those at lower 

 levels. 



The species of tsetse fly associated with sleeping sickness requires 

 a warm, damp atmospliere, and the immediate presence of water. 

 The limit of its altitudinal range is about 4,000 to 5,000 feet. It is 

 found in the true equatorial forests where there is water, and also 

 extends into the adjacent grasslands where there are groups of trees. 

 Sleeping sickness occurs over a vast area in tropical and subtropical 

 Africa. There it causes high mortality, a decreased birtii rate, and 

 is a serious menace to the existence of a large population. In con- 

 sequence of its ravages, the labor supply is being diminished, and the 

 economic development of the country is being retarded. 



Because of its inevitable enervating and enfeebling effects, hook- 

 worm is another tropical and subtropical disease which is a very 

 serious menace in many places. The economic loss is very heavy, 

 perhaps even heavier than that caused by malaria. It has been esti- 

 mated that between GO and 80 per cent of the population of India 

 harbor the parasite. 



Yellow fever, formerly widely prevalent along the tropical shores 

 of Latin America, and occasionally even invading our Gulf coasts, 

 now has its last stronghold in western equatorial Africa, where such 

 splendid work, unfortunately accompanied by the loss of valuable 



