INFLUENCE OF BIFFEEENT CARBOHYDRATES. 49 



EXERCISE XXXVII. 



THE INFLUENCE OF DIFFERENT CARBOHYDRATES ON NITROGEN 

 FIXATION BY AZOTOBACTER. 



1. Make up one liter of "mannite" solution without add- 

 ing the mannite. 



2. Divide into ten 100 cc. portions in 500 cc. flasks. 



3. Make the following additions. 



1 & 2 — 1.5 gms. mannite. 



3 & 4- — 1.5 gms. dextrose. 



5 & 6 — 1.5 gms. glycerine. 



7 & 8 — 1.5 gms. 1% ethyl alcoliol. 



9 & 10 — 1.5 gms. sodium acetate. 



4. Plug and sterilize in the autoclave as usual. 



5. Inoculate each with 1 cc. of a vigorous culture of Az. 

 vinelandii. 



6. Incubate 6-7 days at 20° C. 



7. Add 0.7 gm. Hg. and 20 cc. HjSO^ and determine the 

 nitrogen present by the regular Kjeldaihl process. 



8. The effect of different carbon sources on the amount of 

 nitrogen fixed is thus determined. 



