FLUORIDE OF CALCIUM. 35 



finds it easier to transport his whole family and possessions 

 to the backwoods, where there is a virgin soil, than to send to 

 a distance for his manures to fertilise his land. It has been, 

 then, a most providential event for Europe the discovery of 

 these artificial manures, for we have been consuming our own 

 food, the phosphates of our soils ; and instead of returning 

 them to the land, throwing them into the sea. But even 

 these artificial sources may fail, and then, unless we have 

 learned the art of recovering the phosphates we have used for 

 our life, it will be our turn to share the fate of the cities of 

 antiquity, and men will point to the ruins of our cities, as we 

 now do to those of Babylon, and Tyre, and Sidon." 



I need scarcely add how noble the mission of the agricul- 

 turist is, when, by the light of science and mature experience, 

 he can multiply the plants-, increase according to our require- 

 ments the number of animals and invigorate their constitu- 

 tions, thus tending largely to enhance the prosperity of his 

 country. 



IV. FLUORIDE OF CALCIUM is found in bone in the propor- 

 tion of 3 or 4 per eent, bmt more largely in fossil bones, in 

 which it exists in quantities as high as 12 or 15 per cent. It 

 is believed that this is due to the more ready solution and 

 removal of phosphate of lime from bone by water, charged with 

 carbonic acid, so that the- proportions vary materially accord- 

 ing to the state of preservation of osseous remains. Fluoride 

 of calcium probably renders bones tough by preventing the 

 crystallization of the phosphate. 



V. CAEBONATE OF LIME is a salt entering into the system 

 of animals and plants in the form of a soluble bi-carbonate 

 which is contained in good water. In this soluble form it 

 exists in the secretion of the salivary glands, in the blood, 

 and in the urine of herbivora. It is met with in some parts 

 of the body in a crystalline form, but more largely, as in the 



