14 



THE AVAILABILITY OF VARIOUS COMPOUNDS 

 EFFECTING NITROGEN FIXATION 



It having been previously established that carbohydrates 

 were essential for the maximum efficiency of nitrogen fixation, 

 many sugars have been studied in these investigations. In 

 this connection I have employed the following: mannite, 

 maltose, lactose, saccharose, dextrose, galactose, levulose, 

 arabinose, dulcite, sorbit, raffinose, rhamnose, mannose, ery- 

 thrite, xylose, quercit, glycerine, dextrin, inulin, calcium 

 lactate, and calcium butyrate. These compounds were the 

 best obtainable, mostly Kahlbaum's product, and were ac- 

 curately assayed for nitrogen. 



Ten soils which showed good fixation on mannite were 

 selected for this purpose: numbers 1, 2, 7, 10, 24, 34, 41, 43, 

 47 and 61. These soils were inoculated into Ashby's medium 

 under conditions similar to those followed in the previous 

 experiment, with the one exception that the mannite was 

 replaced by a special sugar or other compound. While it would 

 have been highly desirable to have the data for all the sugars 

 on the ten samples, the prohibitive price on many rendered 

 this quite impossible. An inspection of the table shows the 

 ten highest averages as follows: 



Sorbit 8.32 mg Dulcite 6.21 mg 



Mannite 7.17 mg Arabinose 6.14 mg 



Maltose 6.34 mg Dextrose 5.32 mg 



Mannose 6.32 mg Galactose 5.08 mg 



Levulose 6.28 mg Rhamnose 4.92 mg 



The position held by sorbit is probably only possible 

 because of the remarkable soil number 7. Of the disaccharides, 

 maltose gave the best results, lactose second, and saccharose 

 third. 



An impure sample of maltose which we had in the labora- 

 tory, and which contained 15 mg of nitrogen per two grams of 

 sugar, fixed an average on soils 2, 10, and 41 of 1.02 mg, while 

 the same soils on pure maltose corrected for a very small per- 

 centage of nitrogen, fixed an average of 4.97 mg. This may be 

 accepted as additional testimony that the presence of nitro- 

 genous compounds in considerable amounts is not conducive 

 to high fixation. Mannose, the aldehyde of the alcohol man- 



