STUDY OP SPORE-FORMATION. Ill 



this reason the drop of bouillon should be small and 

 the air-chamber relatively large. 



The cover-slip and hollow-ground slide should be 

 carefully sterilized, and with a sterilized platinum loop a 

 very small drop of bouillon is placed in the centre of 

 the cover-slip. The slip is thea inverted over the hollow 

 depression in the sterilized object-glass and sealed with 

 vaselin. The most convenient method of performing 

 this last step in the process is to paint a ring of vaselin 

 around the edges of the hollow in the slide, and then, 

 without taking the cover-slip up from 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 between the de- 

 pression in the slide and the cover-slip. (See Fig. 20.) 



A drop of sterilized agar-agar may be substituted for 

 the bouillon. It serves to retain the organisms 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 satis- 

 factorily observed. 



It will be noticed that the description of this process 



