106 THE STORY OF GERM LIFE. 



Our cities, then, with our present system of dis- 

 posing of sewage, are draining from the soil the 

 nitrogen compounds and throwing them away. 



In yet another direction must it be noticed 

 that our nitrogen compounds are being lost to 

 plant life viz., by the use of various nitrogen 

 compounds to form explosives. Gunpowder, ni- 

 tro-glycerine, dynamite, in fact, nearly all the ex- 

 plosives that are used the world over for all sorts 

 of purposes, are nitrogen compounds. When they 

 are exploded the nitrogen of the compound is 

 dissipated into the air in the form of gas, much 

 of it in the form of free nitrogen. The basis 

 from which explosive compounds are made con- 

 tains nitrogen in the form in which it can be used 

 by plants. Saltpetre, for example, is equally 

 good as a fertilizer and as a basis for gunpowder. 

 The products of the explosion are gases no 

 longer capable of use by plants, and thus every 

 explosion of nitrogen compounds aids in this 

 gradual dissipation of nitrogen products, taking 

 them from the store of plant foods and throwing 

 them away. 



All of these agencies contribute to reduce the 

 amount of material circulating in the food cycle 

 of Nature, and thus seem to tend inevitably in 

 the end toward a termination of the processes of 

 life; for as soon as the soil becomes exhausted of 

 its nitrogen compounds, so soon will plant life 

 cease from lack of nutrition, and the disappear- 

 ance of animal life will follow rapidly. It is this 

 loss of nitrogen in large measure that is forcing 

 our agriculturists to purchase fertilizers. The 

 last fifteen years have shown us, however, that 

 here again we may look upon our friends, the 

 bacteria, as agents for counteracting this dissi- 



