THE EXAMINATION OF CULTURES 17 



EXERCISE VI 



THE EXAMINATION OF CULTURES 



23. In studying cultures of bacteria, it is necessary to ob- 

 serve 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 

 preparation), and (d) in the dead and stained condition 

 (cover-glass preparation), and (3) the efifect of the growth 

 of the bacteria upon the chemical and the 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. 



24. 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 ofthe 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 prepa- 

 rations. 



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

 examination of cultures and hanging-drop preparations. 



25. Suggestions for the Macroscopic Examination of Cul- 

 tures. — The external appearance of cultures should be ob- 

 served 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 



