BACTERIOLOGICAL TECHNIC 



"5 



dish cover drop into place again; remove the cotton plug from test-tube 

 by grasping it between two fingers (back of fingers toward the test-tube)- 

 make the inoculation (deep stab, shallow stab, or streak); withdraw 

 needle; replace cotton plug; hold needle in flame until glowing red. To 

 prevent the sputtering of the material on the end of the needle, hold near 

 flame until dry and then heat to redness. Singe free exposed end of the 

 tube cotton plug in flame to kill and remove microbes and spores on the 

 outer part of the cotton. The inoculated tubes are then numbered and 

 incubated. In due time the cultural characteristics are noted and the 

 observations entered in a suitable note-book. 



Pig. 41.— Turck ruling of the Thoma-Zeiss hemacytometer. This is especially 

 useful if it is desired to combine the bacterial count with the spore and yeast count. 

 The smaller areas (1-400 sq. mm.) may be used for making the bacterial counts, while 

 the larger areas (1-25 sq. mm.) may be used for making the spore and yeast counts. — 

 (Carl Zeiss.) 



Subcultures may also be made in Petri dishes, on potatoes, in tubes 

 containing bouillon broth, blood serum, milk and other media with or 

 without indicators. 



C. Studying Anaerobic Microbes. — Some microbes have anaerobic tend- 

 encies (facultative aerobes) and some are absolutely anaerobic (obhgative 

 anaerobes). The deep stab culture will show anaerobic tendencies. If 

 such tendency exists, development will be more active near the bottom of 

 tube (in the line of the stab). The culturing of obligadve anaerobes re- 

 quires special apparatus though the methods are not in any way diflScult. 

 The following methods are used: 



a. Deep stab culture. This has already been sufficiently explained. 

 It merely indicates possible anaerobic tendencies. 



b. High-culture methods. Fill the tube of a deep stab culture, shallow 

 stab or streak, with liquid agar or gelatin and incubate in the usual way. 

 The medium to be poured must not be warmer than is absolutely necessary 



