224 DR. R. ANGUS SMITH ON THE PRODUCTION 



of electricity for example, affect the health, and so does 

 the amount of water, of cloud and of light ; but all these 

 causes seem to be different from that insidious poison 

 arising from those organised bodies found neither deep in 

 the earth nor high in the air, but only on the surface of 

 the ground. 



It is now many years since I first began to study these 

 subjects ; and one or two of the facts which I allude to, 

 and which I consider important, were published fourteen 

 years ago; but their significance has not till lately been 

 sufiiciently clear. I observed that the water of soils is 

 sometimes acid and sometimes alkaline ; that on the sur- 

 face generally of our soils it is acid to a small extent, 

 whilst below, when the inorganic salts overpower it, it 

 becomes alkaline. We may say as a rule that all inorganic 

 soils give off their drainage water in an alkaline state. 

 The tendency of plants is to render the soil acid, and if 

 they render it very acid the soil is said to be sour. 

 Drainage will draw off the excess of vegetable juices, and 

 lime will also remove them, as well as other free alkalies. 

 In hot-houses and where rich manures are used, the soil 

 is not always acid, but frequently very alkaline. I have 

 not examined a great many, but where forcing is resorted 

 to with strong manures the result must be and is an alka- 

 line condition. This condition depends on temperature. 

 Having observed some very alkaline soils, I went a few 

 days afterwards for a specimen of water flowing from the 

 surface, without allowing it to pass deep into the strata 

 which would have filtered out its organic matter, and 

 given it alkaline earths. Meantime the weather had 

 changed, and the alkaline water had disappeared, having 

 given place to one that was acid. This was in a peaty 

 district. 



If the soil of our fields were not kept acid, but were 

 kept alkaline and warm, there would arise from it a 



