226 J)R. R. ANGUS SMITH ON THE PRODUCTION 



number of substances produced. These products will vary 

 according to the nature of the substances in the soil, 

 according to the season when one or other substance 

 predominates^ and when one or other substance acts as 

 a ferment. 



It is not necessary to go further than this experiment 

 in order to show that there may arise from soil under 

 certain conditions substances producing the most deso- 

 lating diseases. I suppose this artificial state to be the 

 extreme, such as probably has never happened in an exten- 

 sive district. All other conditions of insalubrity are pro- 

 bably stages of this. It may be said that it was well 

 known that soil retained organic matter^ and that organic 

 matter could putrefy^ but this state of actual decomposition 

 had never before, as far as I know, been observed. By the 

 sense of smell we have found reason to believe that volatile 

 products arise ; disease has also led to this indication, and 

 minute quantities have even by careful experiment been 

 observed; but in the experiment I speak of, the amount 

 rising was gross and unquestionable. I will scarcely ven- 

 ture to speak of the quality of these products. To me 

 they strongly resembled those of putrid flesh or blood, 

 and in that case their composition would probably ally 

 itself to that of protein ; indeed I find that after removing 

 the purely gaseous bodies arising from such decomposition 

 there is left a substance whose carbon and nitrogen bear 

 a relation almost identical with that in protein. But the 

 variety of substances found will probably prove to be 

 extremely great. We can imagine some washed down by 

 the rain, and some removed by the plant. In the same 

 way some classes of malarious diseases may be removed by 

 rain, some caused by more and some by less moisture and 

 heat, and others better removed by the agency of plants 

 and the processes of agriculture. 



The soil is an extremely complex machine ; the balance 



