53 LABORATOEY BACTERIOLOGY. 



EXEECISE XL. 



THE INFLUENCE Or VARYING QUANTITIES OF SUGARS ON 

 NITROGEN-MXATION BY AZOTOBACTER. 



1. Make up 800 cc. of "mannite" solution as described, 

 except thai the mannite is not added. 



2. Divide into eight 100 cc. portions in 500 ce. flasks. 



3. Add sugar in the following amounts : 



1 — 0.25% mannite 



2—0.50% mannite 



3—1.00% mannite 



4—2.00% mannite 



5 — 0.25% mannite 



6—0.50% mannite 



7 — 1.00% mannite 



8—2.00% mannite 



Az. vinelandii. 



Az. chi'oococcum. 



4. Plug and sterilize as usual in the autoclave. 



5. Inoculate with 1 cc. of vigorous cultures of Az. vine- 

 landii and Az. chroococcum. 



6. Incubate 6-7 days at 20° C. 



7. Add 0.7 gm. Hg. and 20 cc. H2SO4, and determine the 

 nitrogen present by the regular KJeldahl method. 



8. Determine the effect of the varying amounts of sugar 

 used on the nitrogen fixed by the pure cultures. 



