186 BACTERIOLOGY. 



the table upon which it rests, invert the hollow over the 

 drop and press it gently down upon the cover-slip. The 

 vaselin causes the slip to adhere to the slide, so that it 

 can be easily taken up. The drop now hangs in the 

 centre of the small air-tight chamber which exists be- 

 tween the depression in the slide and the cover-slip. 

 (See Fig. 38.) 



A very thin drop of sterilized agar-agar may be sub- 

 stituted for the bouillon. It serves to retain the organ- 

 isms in a fixed position, and the process may be more 

 easily followed. 



As soon as finished the preparation is to be examined 

 microscopically and the condition of the organisms 

 noted. It is then to be retained in a warm chamber 

 especially devised for the purpose, and kept under con- 

 tinuous observation. The form of chamber best adapted 

 for the purpose is one which envelops the whole micro- 

 scope. It is provided with a window through which 

 the light enters, and an arrangement for moving the 

 slide about from the outside. The formation of spores 

 requires a much longer time than the germination of 

 spores into bacilli, but with patience both processes may 

 be satisfactorily observed. 



It will be noticed that the description of this process 

 is very much like that which immediately precedes, but 

 differs from it in one respect, viz., that in this manipu- 

 lation we are not making a preparation which is simply 

 to be examined and then thrown aside, but it is an 

 actual pure culture, and must be kept as such, otherwise 

 the observation will be worthless. For this reason the 

 greatest care must be observed in the sterilization of 

 all objects employed. Studies upon spore-formation by 

 this method frequently continue over hours, and some- 



