44 LABOUATOEY BACTERIOLOGY. 



EXEECISE XXXIII. 



THE ISOLATION AND DESCRIPTION OF AZOTOBACTER. 



1. By means of a platinum loop make transfers from the 

 cultures obtained in the preceding experiment into tubes of 

 sterile mannite solution. 



2. Incubate 6-7 days at 20° C. 



3. Then inoculate from these cultures into tubes of sterile 

 water. 



4. Prom each of these dilutions make transfers into three 

 tubes of sterile, liquefied, and cooled (to 40° C.) mannite 

 agar, in series, and plate in the usual way. 



5. Incubate 6-7 days at 20° C. 



6. With a platinum needle, inoculate from several well 

 isolated, dissimilar colonies into tubes of sterile mannite 

 solution. 



7. Incubate 6-7 days at 20° C. 



8. Make microscopic stained and hanging-drop prepara- 

 tions from the pure cultures obtained and describe the char- 

 acteristics of the organisms. 



9. Inoculate from each culture into flasks containing 100 

 cc. of sterile mannite solution. 



10. Incubate 6-7 days at 20° C. 



11. Add Hg. and H^SO^ and digest, determining the 

 nitrogen present by the regular Kjeldahl method. 



12. Describe the growth of each of the organisms on 

 agar plates and in mannite solutions, and identify them. 



