V49-4 MANUAL OF METHODS FOR PURE CULTURE STUDY 



namely: liquid media at 37°; solid media at 37°; liquid media at 21- 

 25°; and solid media at 21-25°. 



Sj)ace is provided on the Standard Chart lor recording ojitimum 

 medium and temperature. This does not ordinarily mean that one 

 must determine the one best medium for the growth of the culture 

 nor the exact degree of temperature at which it grows most rapidly ^ 

 In the first blank one may record such terms as "organic, solid," 

 "organic, liquid," "inorganic, solid" etc., unless it be known that 

 there is one particular medium specially adapted to the organism in 

 question. Under the second blank one may record temperature in 

 general terms, as: "20-25°", "35-40°", "45-50°", or "over 55°." 



It is also important to remember that certain organisms (frequently 

 facultative anaerobes) which do not grow in either solid or true liquid 

 media, will grow in a "semi-solid" medium (that is a nutrient solution 

 in which 0.05-0.1% of agar has been dissolved). It is of course im- 

 portant that such organisms be studied under optimum conditions; 

 and for their study the procedures given in this Manual should 

 ordinarily be modified by using media containing 0.05-0.1% agar 

 instead of the usual liquid or solid media. 



Thermal death point, as called for under "Temperature Relations" 

 on the back of the Chart, is undoubtedly- best determined with the use 

 of capillary tubes. Short pieces of thin-walled tubing having an in- 

 ternal diameter of 1-1.5 mm. are filled with the culture (consisting 

 mostly of spores, if it is a spore-former) and are heated for varying 

 periods of time at the temperatures under investigation. After heat- 

 ing, each tube is broken into a tube of a medium in which the organ- 

 isms grow well. A tabulation of results gives a good idea of the ther- 

 mal death point. This procedure requires careful attention to detail; 

 and one should consult the description of it by Magoon (1926). 

 Results are most valuable if the length of time before death is re- 

 corded: in which case, this becomes a test for Thermal death time. 



Incubation 



Cultures should be incubated at or near the optimum temperature 

 of the organism or organisms under investigation. As a rule it is not 

 necessary, however, to know the exact optimum temperature of each 

 organism. If the laboratory is equipped with a series of incubators 

 running at 20°, 25°, 30°, and 37°C, the tem])erature requirements of 

 practically all bacteria except the thermophilic forms can be very 

 satisfactorily met. Room temperature is sometimes used in place of 25°; 

 but is not to be recommended because of its uncontrollable variations. 



Length of incubation varies and is specified on the Chart under 

 many of the tests. In cases where it is not specified one should 

 observe the following general rule: On the day when good growth 



