QUESTIONS 183 



QUESTIONS. 



1. What is the general principle underlying the bacteriologic examination of 

 soil, water, milk? 



2. What is the principle on which the method for quantitative bacteriologic 

 air examination is based ? 



3. What is meant by a quantitative, by a qualitative bacteriologic exami- 

 nation of soil, water, air, etc.? 



4. What method is used when soil is to be examined for the presence of 

 tetanus bacilli ? 



5. How can air be examined for the presence of tubercle bacilli? 



6. Describe the arrangement and use of a W^olffhiigel counting apparatus. 



7. What is a square centimeter; what a square millimeter? What is a cubic 

 centimeter ? 



8. How many colonies are in the culture medium of a Petri dish 8 cm. in 

 diameter if on an average each square centimeter contains twenty-three colonies? 



9. What is an Esmarcjh roll-tube? 



10. Describe a simple method of approximately estimating the number of 

 germs in air by the aid of exposed Petri dishes. 



11. Describe another method by the aid of large Erlenmeyer flasks filled with 

 water. 



12. What is a liter? What is its equivalent in pints? 



13. Describe Hesse's method of quantitative bacteriologic air examination. 



14. Describe Eyre's method of aspirating air for a quantitative bacteriologic 

 analysis. 



15. Describe the method of 'using sand or sugar as filters for catching the 

 bacteria in aspirated air. 



16. What is the Sedgwick-Tucker modification of the air-filtering tube? 



17. How are flasks used in collecting water for quantitative bacterial analysis 

 to be sterilized and handled before use ? 



18. How can water running from a faucet be prevented from washing down 

 bacteria from the latter into the collecting flask ? 



19. How is water collected from a river or pond? 



20. What devices are used for collecting water from a particular depth? 



21. Describe the method of obtaining definite amounts of water from the 

 collecting bottles for the inoculation of culture media. 



22. WTiat procedure is employed with a specimen of water containing many 

 bacteria in order to avoid getting an uncountable number of colonies in the 

 Petri dishes? 



23. At what temperature and how long shall the Petri dishes be kept before 

 the count of the colonies is undertaken ? 



24. Why do quantitative bacterial soil examinations furnish very unreliable 

 figures ? 



25. Describe the method of collecting soil from the surface. Also method of 

 obtaining soil from any desired depth. 



