DIFFKKKNT KINDS OF MAN CUE. 311 



"It is rather a reflection ou our scicuce and practical skill," said 

 the Doctor, " but it looks at present as though the only plan to 

 adopt in large cities is to use enormous quantities oi^ water and 

 wash the stuff into the rivers and oceans for the use of aquatic 

 plants and fishes. The nitrogen is not all lost. Some of it comes 

 back to us in rains and dews. Of course, there are places where 

 the sewage of our cities and villages can be used for irrigating 

 purposes. But when water is used as freely as it ought to be used 

 for health, the sewage is so extremely poor in fertilizing matter, 

 that it must be used in enormous quantities, to furnish a dressing 

 equal to an application of 20 tons of stable-manure per acre." 



" If," continued the Doctor, " the sewage is used merely as water 

 for irrigating purposes, that is another question. The water itself 

 may often be of great benefit. This aspect of the question has not 

 received the attention it merits." 



PERUVIAN GUANO. 



Guano is the manure of birds that live princii^ally on fish. 



Fish contain a high percentage of nitrogen and phosphoric acid, 

 and consequently when fish are digested and the carbon is burnt 

 out of them, the manure that is left contains a still higher percent- 

 age of nitrogen and phosphoric acid than the fish from which it 

 was derived. 



Guano is digested fish. If the guano, or the manure from the 

 birds living on fish, has been preserved without loss, it would con- 

 tain not only a far higher percentage of nitrogen, bat the nitrogen 

 would be in a much more available condition, and consequently 

 he more valuable than the fish from which the guano is made. 



The difference in the value of guano is largely due to a difference 

 in the climate and localit}' in which it is deposited by the birds. 

 In a rainless and iiot climate, where the bird-droppings would dry 

 rapidly, little or no putrefaction or fermentation would take place, 

 and there would be no loss of nitrogen from the formation and 

 escape of ammonia. 



In a damper climate, or where there was more or less rain, the 

 bird droppings would putrefy, and the ammonia would be liable to 

 evaporate, or to be leached out by the rain. 



Thirty years ago I saw a quantity of Peruvian guano that con- 

 tained more than 18 per cent of nitrogen. It was remarkably light 

 colored. Tou know that the white part of hen-droppings consists 

 priacipaUy of uric acid,which contains about 33 per cent of nitrogen. 



For many years it was not difficult to find guano containing 13 

 per cent of nitrogen, and genuine Peruvian guano was the cheap- 



