NITROGEN-FIXING BACTERIA 131 



In the ordinary processes of vegetation there is a gradual draining of 

 the soil and a passing of nitrogen into the sea; the products of 

 decomposition pass from the soil by this drainage, and are " lost " as 

 far as the soil is concerned. Many of the methods of sewage dis- 

 posal are in reality depriving the land of the return of nitrogen, 

 which is its necessity. Again, nitrogen is freed in explosions of 

 gunpowder, nitroglycerine, and dynamite, for whatever purpose they 

 are used. Hence the great putrefactive " loss " of nitrogen, with its 

 subsidiary losses, contributes to reduce this essential element of all 

 hfe, and if there were no method of bringing it back again to the 

 soil, it would seem that plant life, and therefore animal life, would 

 speedily terminate. 



3. Nitrogen-Fixing- Bacteria 



It is at this juncture, and to perform this vital function, 

 that the nitrogen-fixing bacteria play their wonderful part: they 

 help to recover the free nitrogen and fix it in the soil. Excepting a 

 small quantity of combined nitrogen coming down in rain and in 

 minor aqueous deposits from the atmosphere, the great source of the 

 nitrogen of vegetation is the store in the soil and subsoil, whether 

 derived from previous accumulations or from recent supplies by 

 manure. 



Sir William Crookes has pointed out the vast importance of 

 using all the available nitrogen in the service of wheat production.* 

 The distillation of coal in the process of gas-making yields a certain 

 amount of its nitrogen in the form of sulphate of ammonia, and this, 

 like other nitrogenous manures, might be used to give back to the 

 soil some of the nitrogen drained from it. But such manuring 

 cannot keep pace, according to Sir W. Crookes, with the present 

 loss of fixed nitrogen from the soil. We have already referred to 

 several ways in which " loss " of nitrogen occurs. To these may well 

 be added the enormous loss occurring in the waste of sewage when it 

 is passed into the sea. As the President of the British Association 

 pointed out, the more widely this wasteful system is extended, 

 recklessly returning to the sea what we have taken from the land, 

 the more surely and quickly will the finite stocks of nitrogen, locked 

 up in the soils of the world, become exhausted. Let us remember 

 that the plant creates nothing in this direction ; there is no com- 

 bined nitrogen in wheat which is not absorbed from the soil, and 

 unless the abstracted nitrogen is returned to the soil, its fertility 

 must be ultimately exhausted. When we apply to the land sodium 

 nitrate, sulphate of ammonia, guano, and similar manurial substances, 

 we are drawing on the earth's capital, and our drafts will not be 



* The Wheat Problem, 1899. 



