QUANTITATIVE BACTERIAL ANALYSIS OF AIR 221 



7. Attach the aeroscope (lower end of carbon tube), to 

 the aspirator so that the aspirated air will be filtered through 

 the sand. 



8. Remove the cotton plug from the upper end of the 

 aeroscope and filter 8 liters of air in 

 approximately eight minutes. 



9. Using " aseptic " precautions, trans- 

 fer as much sand as possible to one of the 

 tubes of sterile salt solution. 



10. Mix well by bumping the tube 

 against the hand at least fifty times (do 

 not wet the cotton plug). 



11. Then, with a sterile 1 c.c. pipette, 

 transfer 1 c.c. of the suspension to each 

 of four Petri dishes and pour plates. 



12. Incubate two plates at 37 C. for 

 two days, and the remaining two plates 

 at room temperature for five days. 



13. Count at the end of these respec- 

 tive periods and determine the number 

 of bacteria per liter. How do your counts 

 compare with air counts obtained by 

 other students? from other data? (See 

 Marshall's Microbiology, p. 789.) 



Make separate counts of molds and 

 identify them as far as possible. 



14. Make sub-cultures of different 

 types on agar and study their cultural 

 characteristics on this medium. 



15. Transfer these cultures to tubes of 

 broth and litmus milk and note their 



action on these media. Draw conclusions from these 

 results. 



16. What morphological types are found? Are any of 

 the types of bacteria present constantly found in air? What 

 are the sources of microorganisms in the air? 



FIG. 47. Modified 

 Standard Aero- 

 scope. (Ruehle 

 and Kulp.) 



