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remain, are not only liable to become diseased, but are quite 

 certain to suffer in health, more or less, from constant ex- 

 posure. The habit of building most towns on the banks of 

 some river or stream — done originally, no doubt, for the 

 convenience of a supply of water, or for the transport of 

 merchandise — has been the main cause that has rendered 

 our principal towns so unhealthy, and our scale of average 

 duration of life so low. There are certainly no means known 

 at present calculated to obviate the evil entirely. Sheltered 

 valleys and river courses will always be, from time to time, 

 the scenes of stagnant atmospheres, fogs, and, to a greater 

 or less extent, of a badly-drained soil. Towns in such 

 localities must, at all times, be subject to the evils which 

 attend such obvious sources of infection. A great deal, 

 however, will depend on the nature of the soil on which the 

 town is built, as well as on its exposure to these atmospheric 

 influences. There are some soils so retentive of any liquid 

 drainage which may soak into them, and so impervious to 

 atmospheric air, that after a few years the whole surface 

 acquires the condition of a putrid bog, while others are 

 built upon a naturally or artificially porous surface, with a 

 retentive clay subsoil, so that drainage can soak down, and 

 convert the whole into a putrid mass, similar in condition to 

 a stagnant pond partly filled with rubbish. In such cases 

 it would be unnecessary for me to state that the results of 

 putrefaction would be poured into the atmosphere in abun- 

 dance. In some cases, however, the soil is sufficiently porous 

 to allow all excess of moisture to drain away, and thus to 

 leave the surface porous and permeable to the atmosphere. 

 In such instances the process of putrefactive decomposition 

 would be entirely prevented, and the healthy one of decay 

 substituted in its stead. It is evident, therefore, that we 

 should endeavour to imitate this natural process by artificial 

 drainage as far as possible, for we should thereby prevent 



