166 GENERAL MICROBIOLOGY 



acid crystals; then place 10 c.c. of 10% NaOH in the cover 

 of the dish. (The cotton prevents a too rapid reaction be- 

 tween the chemicals.) 



5. Seal at once by packing the space between the cover 

 and bottom air tight with modeling clay. Then mix the 

 chemicals. 



6. Place all six plates at room temperature. 



Note. In the reaction which takes place between pyrogallic acid 

 and NaOH, oxygen is used and an anaerobic condition is established 

 within the culture dish (exact reaction not known.) 



7. Count the organisms after seven days. Estimate the 

 number of different types of colonies developing under the 

 varying conditions of air supply and note growth. Con- 

 clusions? 



8. Compare your results with those of others and draw 

 conclusions. 



9. Make gelatin stabs of three or four of the predomi- 

 nant types of colonies and cultivate anaefobically by 

 Hesse's method. What types of organisms are these 

 morphologically and culturally? 



10. Are any types found on aerobic plates which are 

 lacking on the anaerobic plates and vice versa? 



What type of anaerobe is frequently found in horse 

 manure? 



11. When do anaerobic conditions exist in milk? In 

 soil? Is this beneficial or otherwise in each case? What 

 relation may there be between age of milk and type of colo- 

 nies? Can this same relationship apply in the case of 

 soil? 



12. What other methods may be used for obtaining 

 anaerobic conditions for microbial growth? Name the 

 obligate anaerobes. 



13. How is an organism isolated which is tolerant of an 

 amount of oxygen less than that of the atmosphere, but will 

 not grow under strictly anaerobic conditions? 



14. State your results for the experiment in detail and 



