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attention to that inorganic constituent of plant-food 

 than to any of the others. 



We possess considerable quantities of this valuable 

 substance in guano, the deposits of sea-birds, which 

 have been accumulating for ages on several islands 

 where rain is scarcely known. These deposits are 

 truly treasures reclaimed by mature from the depths 

 of the ocean, the food of these birds being entirely 

 derived from it ; they are treasures which we can 

 use with a clear conscience for restoring the fertility 

 of our soils. But they are not inexhaustible ; they 

 are diminishing year by year, and will be consumed 

 before long ; and what then ? 



We will then have to recognize the necessity of 

 utilizing what lies at our very doors, and consider 

 the chief sources of phosphoric acid which are avail- 

 able to us, and whence it must ultimately reach the 

 soil. These sources are firstly, the bones of man 

 and animal, the frame -work of their bodies which 

 nature constructs from the minute quantities of lime 

 and phosphoric acid contained in their food ; and 

 secondly, their refuse, solid and fluid, which, when 

 they arrive at maturity, contains to the minutest por- 

 tion of a grain the ashes of the food consumed. So 

 that every ounce we neglect to gather, every gallon 

 we throw away, is so much total loss to the capital 

 which nature has so wisely provided for our main- 

 tenance in the arable soil of our fields. 



The waste of these natural fertilizers is, as I have 



