THE EXAMINATION OF CULTURES 17 
EXERCISE VI 
THE EXAMINATION OF CULTURES 
24. In studying cultures of bacteria it is necessary to 
»bserve very carefully (1) the macroscopic appearance of the 
srowth in or upon the media, (2) the microscopic appearance 
of the bacteria in (a) the living condition (hanging-drop prep- 
ation) and (4) in the dead and stained condition (cover- 
slass preparation), and (3) the effect of the growth of the 
racteria upon the chemical and physical properties of the 
nedium. To determine these the cultures must be kept 
inder observation for several days and often for several weeks. 
\ careful record should be made of the changes observed in 
he appearance of the cultures. [Illustrate with drawings. 
25. Work for this exercise. Examine carefully and de- 
icribe fully the appearance of the bouillon, agar, and gelatin 
vultures made in Exercise V. 
Determine the reaction of the bouillon culture and note 
vhether there is any change in its consistence (viscidity). 
Make a hanging-drop preparation from each culture and 
*xamine and describe the appearance of the bacteria in 
2ach. 
Make a drawing of the gelatin and slant-agar cultures and 
so of a few of the bacteria in one of the hanging-drop 
»reparations. 
Read the paragraphs in one or more text-books on the 
‘xamination of cultures and hanging-drop preparations. 
26. Suggestions for the macroscopic examination of cultures. 
Che external appearance of cultures should be observed and 
.oted on the day after they are made and on each succeeding 
lay until the growth ceases. In bouillon cultures note the 
ppearance of the liquid, whether uniformly, faintly, or heavily 
louded, turbid, clear, or clouded with flocculent masses held 
