Mr. T. Hopkins's Observations on Malaria. 105 



to any particular country. It is indeed distributed extensively 

 over the surface of the earth. Asia, Africa, and America feel 

 the scourge in a more violent degree than it is felt in any part 

 of Europe: the plains of Bengal, the vallies of the African 

 coast, and the West Indian islands are infected in a more 

 deadly degree than even Italy ; it is therefore reasonable to 

 infer that the locality of gases or minerals is not connected 

 with its production. It is found too in climates having dif- 

 ferent temperatures to those of the countries just named, as 

 on the eastern coast of England, in France, and Holland : 

 very high temperature therefore does not seem essential to its 

 production. But though not absolutely requisite to its pro- 

 duction, high temperature appears to increase its virulence, 

 the injurious effects on the human constitution having a pal- 

 pable relation to the temperature of the atmosphere. Thus 

 in Lincolnshire, France, and Flolland, its operation is slow, 

 and it requires considerable time to produce fatal effects; but 

 in the Campagna of Rome, it is said that a single night passed 

 within the full influence of the pest endangers life. In the 

 jungles of Bengal it is fully as bad as in the Campagna, and in 

 the vallies of the western coast of Africa the greater number 

 of the crew of a ship have been known to die in a short time. 

 Thus it becomes apparent that the virulence of the fever 

 arising from malaria is great in proportion to the heat of the 

 climate. 



Yet great heat alone does not seem capable of producing the 

 poison. However high the temperature may be, provided 

 it is not accompanied by moisture, the air is found to be 

 health}'. The plains of Russia are hotter in summer than the 

 marshes of Holland, but no malaria is found in tlie former, 

 while it abounds in the latter, because the plains of Russia 

 are dry as well as hot. Rome is only seven degrees hotter 

 than Moscow in the hottest month of the year, yet malaria 

 is virulent in the one, while it does not exist in the other. In 

 the sandy deserts of Asia and Africa we have perhaps the 

 hottest climates of the globe, but as these deserts are at the 

 same tiuie dry malaria is not prevalent in them. The infer- 

 ence is that heat alone will not produce malaria, but that the 

 presence of moisture also is necessary. 



Dr. Macculloch admits, " that the extreme of evil from 

 malaria occurs in tropical climates, it appearing almost j)ro- 

 portioned to the heat of the climate, and, what is important 

 to observe, to the moisture also." He also remarks that 

 " Egypt is free Irom the fever arising from malaria except at 

 the period ol" the subsidence of the Nile, unless where, as at 

 Damietta, the cultivation of rice is pursued." But the Doctor 



