154 Food from the Soil 



Nitrates are very soluble, and in damp soil they 

 are formed and dissolved so quickly as seldom to be 

 visible. But it is not so in regions where rain falls 

 either at certain seasons only, or very rarely. The 

 most fertile soils of Bengal, for instance, are often 

 covered during the dry season with a white crust of 

 some of these salts, chiefly potassium nitrate, other- 

 wise called nitre and saltpetre. The crust vanishes as 

 soon as the rain comes, being dissolved and washed 

 into the soil, which is so rich as to bear two or three 

 crops a year. 



Wherever these nitrates are formed, whether, as in 

 England, they are dissolved almost at once, or whether, 

 as in dry lands, they accumulate and encrust the soil, 

 they are formed by the decay of animal and vegetable 

 matter. And what, it may be asked, causes this 

 decay ? Not the action of the air ; for in perfectly pure 

 air organic substances do not decay. The change is 

 brought about by the action of living organisms, 

 invisible, but very potent in their effects. 



We have all heard enough about ' germs ' of late to 

 know that they swarm in the air ; but they also swarm 

 in all the moist places of the earth. Some few classes 

 of them are dangerous to man, and produce diseases 

 of various kinds; others are not only harmless, but 

 productive of the greatest good. 



All decay, fermentation, or putrefaction, whichever 

 we call it, is their work ; and when we say ' work,' all 

 that is meant is their living, growing, multiplying, 

 which they cannot do vf'xihoni Jeeding. There is an 

 immense variety of them, and they produce different 

 results according to their different modes of feeding. 

 The yeast which is put into dough, the * mould ' which 



