428 THE PRINCIPLES OF SOIL MANAGEMENT 



portation of a great bulk and weight of material, 

 has led to numerous efforts to inoculate soil by means 

 of pure cultures. The pure culture may also make it 

 possible to bring to the soil bacteria of greater physio- 

 logical efficiency than those already there. 



The first attempt at inoculation by pure cultures 

 was made in Germany, the cultures being sold under the 

 name of "Nitragin." Careful experiments made with 

 this material previous to the year 1900 did not show 

 it to be very efficient; but, of recent years, improve- 

 ments in the method of manipulating the cultures 

 have resulted in much greater success. In " Nitragin," 

 the medium used for growing the organisms is gelatin, 

 and, before use, this was formerly dissolved in water; 

 but now a solution of greater density is used in order 

 to prevent a change of osmotic pressure, which may 

 cause plasmolysis and result in the destruction of the 

 bacteria. 



Within recent years, a number of cultures for soil- 

 inoculation have been offered to the public. The first 

 of these utilized absorbent cotton to transmit the 

 bacteria in a dry state from the pure cultures in the 

 laboratory to the user of the culture, who was to 

 prepare therefrom another culture to be used for 

 inoculating the soil. Careful investigation of this 

 method showed that its weakness lay in drying the 

 cultures on the absorbent cotton which frequently 

 resulted in the death of the organisms. More recently, 

 liquid cultures have been placed on the market in this 

 country, but they have not yet been sufficiently well 

 tested to prove their efficiency. It is undoubtedly 



