THE EXAMINATION OF CULTURES I/ 



EXERCISE VI 



THE EXAMINATION OF CULTURES 



24. In studying cultures of bacteria it is necessary to 

 observe very carefully (i) the macroscopic appearance of the 

 growth in or upon the media, (2) the microscopic appearance 

 of the bacteria in (a) the living condition (hanging-drop prep- 

 aration) and (b) in the dead and stained condition (cover- 

 glass preparation), and (3) the effect of the growth of the 

 bacteria upon the chemical and physical properties of the 

 medium. To determine these the cultures must be kept 

 under observation for several days and often for several weeks. 

 A careful record should be made of the changes observed in 

 the appearance of the cultures. Illustrate with drawings. 



25. Work for this exercise. Examine carefully and de- 

 scribe fully the appearance of the bouillon, agar, and gelatin 

 cultures made in Exercise V. 



Determine the reaction of the bouillon culture and note 

 whether there is any change in its consistence (viscidity). 



Make a hanging-drop preparation from each culture and 

 examine and describe the appearance of the bacteria in 

 each. 



Make a drawing of the gelatin and slant-agar cultures and 

 also of a few of the bacteria in one of the hanging-drop 

 preparations. 



Read the paragraphs in one or more text-books on the 

 examination of cultures and hanging-drop preparations. 



26. Suggestions for the macroscopic examination of cultures. 

 The external appearance of cultures should be observed and 

 noted on the day after they are made and on each succeeding 

 day until the growth ceases. In bouillon cultures note the 

 appearance of the liquid, whether uniformly, faintly, or heavily 

 clouded, turbid, clear, or clouded with flocculent masses held 



