NITROGEN FOR MICROBIAL GROWTH 173 



Winogradski's medium for nitrate formation (inorganic 

 nitrogen combined with an inorganic acid) . 



Winogradski's medium for symbiotic nitrogen-fixation 

 (nitrogen-free) . 



Cultures. B. subtilis; Ps. radicicola; Aspergillus niger; 

 Sacch. ellipsoideus. 



Method. 1. Inoculate heavily a tube of each medium 

 with Ps. radicicola. Proceed likewise with the three remain- 

 ing organisms. 



2. Record the growth at the end of five days. What 

 conclusions may be drawn? 



3. Compare the formulae of the different media given 

 above. Organic nitrogen is present in the radical NH2, 

 inorganic, NH4. 



4. What is the explanation for the growth of one organ- 

 ism and not another on a certain medium? 



Do the organisms obtain their carbon from an organic 

 or an inorganic compound in each case? Is organic or in- 

 organic nitrogen the most available in each case? What 

 is the value of such a medium? Why are other chemicals 

 added besides the main nutrient? 



Why is distilled water used in all these media? To 

 what does the term " auxanography " refer? 



5. Give your results in detail and draw any conclusions 

 warranted. What practical applications may be made of 

 the above? 



REFERENCES 



MARSHALL: Microbiology, pp. 91-93, 99, 242, 362. 

 LAFAR: Technical Mycology, Vol. I, pp. 361, 468. 

 LOHNIS: Laboratory Methods in Agricultural Bacteriology, p. 58. 



