80 THE TREATMENT OF DISEASES. 



Malaria is seldom met with in cold climates, nor in the winter months of mor? 

 temperate regions. Decomposing vegetable matter is not in itself sufficient to 

 produce malaria, a certain amount of moisture being essential. It is generally 

 believed that in the case of marshes the poisonous emanations proceed from those 

 parts which are only occasionally covered with water, and then undergo a process 

 of gradual evaporation, and not from those which are more or less completely 

 submerged. Malaria loves low-lying districts, and in temperate climates seldom 

 ascends above a height of 500 feet. It is always found in the greatest 

 intensity near the ground, but why this is we don't quite know. It may be due 

 to the action of gravity, or it may be that the poison is entangled by the fog, 

 and earned down by it. It is well known that in malarious districts it is 

 much more dangerous to sleep on the ground-floor than in the upper storeys. It has 

 often been found that in barracks the number of soldiers taken ill with ague 

 in the lower apartments is greatly in excess of those who suffer in the upper, 

 and consequently in many places abroad it is customary, if possible, to leave the 

 ground-floor untenanted. Malaria is capable of being carried by the wind in a 

 manner analogous to that of fogs. This is a matter of no little importance in 

 tropical climates, where the wind frequently blows for days, weeks, or even months 

 together from the same quarter. When malaria exists above its ordinary level, a 

 careful examination will usually show that it has been carried up ravines by 

 means of currents of air, or that it is due to some local cause. Sometimes even 

 the poison has been blown right over a hill, and dropped, so to speak, on the other 

 side. Malaria has been found to act with by far the greatest intensity at night. It 

 may be that it is at these times more copiously evolved, or it may be that at night 

 the system is more susceptible to its influence. 



It is a curious though well-established fact that malaria loses its noxious pro- 

 perties by passing over even a small surface of water, particularly if it be salt water. 

 It would seem as if the water dissolved it, and this is in all probability the case, for 

 in India it is a common belief that water over which malaria has passed is quite 

 unfit for drinking purposes, and that when taken into the system it is capable of 

 producing not only ague, but dysentery, and even cholera. Belts of trees exert almost 

 as powerful an influence as sheets of water in arresting the progress of marsh miasm. 

 It is supposed that foliage has a special attraction for malaria, and that it has the 

 power of decomposing it. It is said that woods and groves were first regarded 

 as sacred from the protective powers which they exert from ague, and in many 

 regions settlers live with impunity close to the most pestiferous marshes, provided 

 only that a belt or screen of trees be interposed. Such, then, is the poison which 

 causes ague. 



Every one is susceptible to the action of the poison, and consequently every one 

 is liable to suffer from ague. Neither the old nor the young can claim exemption 

 from the effects of its pernicious influence, and the malady attacks indifferently 

 children of a few days old and men of threescore and ten. Practically the largest 

 number of cases occur in men in the prime of life, and for the very obvious reason 

 that they, the pioneers of civilisation, are more likely to be exposed to the influence 

 of the poison than are women or old men and children. 



