102 CLINICAL BACTERIOLOGY. 



of pyrogallic acid, 10 cu. cm. of I per cent, potassium 

 hydroxid). (Fig. 33.) Pyrogallic acid has the peculiarity 

 of taking up oxygen, and in this way the space in which 

 the cultures are exposed is quickly freed of oxygen. 



Raw eggs also may be employed for anaerobic culture. 

 One extremity of the egg is thoroughly cleansed with 

 mercuric chlorid and sterile water, a puncture is made with 

 a needle sterilized in the flame and still hot, and with the 

 platinum needle a portion of the pure culture is introduced 

 into the interior of the egg. The small opening made is 

 then closed with hot sealing-wax. 



MICROSCOPIC EXAMINATION AND STAINING OF BACTERIA. 



To examine bacteria in the living state in the hanging 

 drop, a small drop is removed from a fluid culture by 

 means of the platinum loop sterilized in the flame, and it is 

 then placed in the center of a cover-slip carefully cleansed 

 with alcohol. (.Fig. 34.) The cavity of a slide that has been 



Fig. 34. The " hanging drop" seen from above and in profile (Mallory and Wright). 



excavated at its center is surrounded with vaselin, and 

 the slide is pressed face down upon the cover-slip, so that 

 the drop is suspended exactly in the center of the cavity. 

 If it be desired to prepare a hanging drop from a solid 

 culture, a drop of sterile water or of bouillon is first placed 

 upon the cover-slip, and to this is added a minimal amount 

 of the bacteria to be examined. It is useful in some cases 

 to add to the hanging drop a small amount of a dilute 

 staining solution : e. g., a carbol-fuchsin solution (p. 104) 

 diluted four or five times. The small amount of coloring- 

 matter added does not influence the vital activity of the 

 bacteria. These are stained faintly, but the motile varieties 



