xvir UTILISATION OF THE SOIL 201 



learned to use the soil aright is too long to tell 

 here. All that we can do is to pick out a few 

 famous names, and show with what steps in progress 

 these names are associated. Of special importance 

 are the questions associated with the problem of 

 where plants get the nitrogen they require to make 

 their proteids (see p. 117), and we shall restrict 

 ourselves in this chapter to that problem. 



We will begin with the work of Baron Liebig. 

 Liebig was a great German chemist who was born 

 in 1803 and died in 1873. He made many great 

 discoveries ; he invented the first meat extract ; he 

 compounded a food for infants ; he did many other 

 things for his country and for the world. All that 

 we need stop to learn about him here, however, is 

 that he was the first to state a consistent theory 

 about the food of plants in relation to farming. 

 This theory was called Liebig's " Mineral Theory." 

 Theory is not perhaps the best word to apply to it, 

 but it was the word which was used. 



It was not a theory in the sense of being 

 spun from his imagination without any relation 

 to actual fact. A scientific theory is an attempt 

 to explain results obtained by observation and 

 experiment. Liebig first did something. What 

 he did was to burn many plants to burn 

 them under' special conditions and with great care. 

 He burnt plants from many different localities, and 



