SECOND REPLY. 171 



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manner in which they have been formed. The peaty soil 

 originates from the decomposition of organic substances in 

 the presence of much water. The consequence of this is, 

 that the water takes up and carries away all the soluble 

 salts which were contained in those organisms, so soon as 

 ever they are set free. In the garden soil, on the contrary, 

 all those soluble salts remain behind, come immediately into 

 the possession of the plants, and, under a rich culture 

 of the soil, accumulate in them to an extraordinary 

 degree, while the organic constituents, through uninter- 

 rupted decomposition, are continually diminished in quantity, 

 and so can never accumulate in the way they do in the 

 peat or bog soils, where the presence of water, after a 

 certain time, restrains or very much retards the further 

 progress of decomposition. A more striking proof of the 

 correctness of the new views of the nutrition of plants 

 could not easily be given, than these statements ; views 

 which were almost simultaneously established and made 

 known by one of the most distinguished chemists, Liebig, 

 and one of the most eminent of practical agriculturalists, 

 Boussingault. 



But I must take leave to return once more to the ques- 

 tion which was first raised : " What does Man live upon ?" 

 We have seen that the nutrient fluids contained in his 

 body, that muscles, skin, and the gelatine which forms the 

 basis of bones, are essentially produced from substances 

 containing nitrogen, which the plants furnish to him as 

 food. But gelatine alone does not complete the bony 

 structures; we find in these, besides the gelatine, the 

 so-called bone-earth, a compound of carbonate aud phos- 

 phate of lime. This it is to which the bone owes its 

 solidity, its hardness, through which alone it is fitted to 



