126 Bacteria in Relation to Country Life 



deprived of its fertility, and loses, in time, its power to 

 produce profitable harvests when none of the fertiUty 

 is restored. 



It has been estimated by Crookes that England alone 

 wastes in the sewage and drainage of her cities, nitrogen 

 to the value of $80,000,000 a year. It has been computed, 

 also, that the conversion of 90 per cent of the nitrogen 

 in the sewage into nitrates, and their utilization, would 

 add $70,000,000 annually to the wealth of England. 

 We see, thus, that the value of combined nitrogen and of 

 other plant-food drained away from the cities, towns 

 and villages, must be truly enormous. Hilgard states 

 that nearly 5,000,000,000 tons of mineral matter in 

 solution are annually removed by the rivers from the 

 earth's surface, and that the amount of sediment simi- 

 larly carried away is much greater. It is safe to assume 

 that the drainage from human habitations forms an 

 appreciable portion of the substances thus constantly 

 added to the sea. 



Knowledge of these facts has naturally encouraged 

 attempts to utilize the manurial ingredients of sewage 

 for crop-production. Efforts have not been wanting 

 to encourage the utilization of the sludge obtained by 

 treating sewage with lime, alumina, or salts of iron. How- 

 ever, the fertilizers manufactured by these processes 

 did not meet with favor among farmers, and the cost of 

 their preparation rendered profitfe,ble production diffi- 

 cult. From time to time, enthusiasts still appear who 

 would, in one way or another, extract the valuable 

 fertilizer constituents from sewage. 



But, while the extraction of the manurial constituents 



