SPORE-FORMATION. 177 



it is rapid and darting. The molecular tremor may be 

 seen with non-motile and with dead organisms. 



NOTE. Prepare three hanging-drop preparations 

 one from a drop of dilute India-ink, a second from a 

 culture of micrococci, and a third from a culture of the 

 bacillus of typhoid fever. In what way do they differ? 



STUDY OF SPOKE-FORMATION. The hanging-drop 

 method just mentioned is not only employed for detect- 

 ing the motility of an organism, but also for the study of 

 its spore-forming properties. 



Since with aerobic organisms spore-formation occurs, 

 as a rule, only in the presence of oxygen, and is induced 

 more by limitation of the nutrition of the organisms 

 than by any other factor, it is essential that these two 

 points should be borne in mind in preparing the drop 

 cultures in which the process is to be studied. For 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 then inverted over the hol- 

 low depression in the sterilized object-glass and sealed 

 with vaselin. The most convenient method of perform- 

 ing 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 vaseliu 

 causes the slip to adhere to the slide, so that it can be 

 easily taken up. The drop now hangs in the centre of 



