SOME GENERAL PRINCIPLES 55 



compared with the many failures. But it is now 

 believed that these cultures can be prepared and used 

 so as to be generally effective and without excessive 

 cost to the grower. 



In preparing cultures it has been found that by 

 gradually reducing the amount of nitrogen in the 

 culture of media, it is possible to increase the nitro- 

 gen fixing power in these germs from five to ten 

 times as much as usually occurs in nature. It is now 

 known that the bacteria thus grown upon nitrogen 

 free media retain high activity if carefully dried and 

 then revived in liquid media at the end of the vary- 

 ing lengths of time. Some absorbent is used to soak 

 up the tubercle-forming organisms. The cultures 

 are then allowed to dry, and when in that condi- 

 tion they can be safely sent to any part of the coun- 

 try without losing their efficacy. It is necessary to 

 revive the dry germs by immersing them in water. 

 By adding certain nutrient salts the bacteria are 

 greatly increased if allowed to stand for a limited 

 time — as short, in some instances, as 24 hours. The 

 culture thus sent out in a dry form, and no larger 

 than a yeast cake, may thus be made to furnish bac- 

 teria sufficient to inoculate not less than an acre of 

 land. It is stated that the amount of inoculating 

 material thus obtained is only limited by the quan- 

 tity of the nutrient water solution used in increasing 

 the germs, so that the cost of inoculating land by 

 this process is not large. The culture may be applied 

 by simply soaking the seed in it, by spraying the 

 soil, or by first mixing the culture into earth, spread- 

 ing it over the field and then harrowing it. Inocu- 



