STUDY OF SPORE-FORMATION. 209 



tion of spores into bacilli, but with patience both proc- 

 esses 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- 

 times days, and contamination must, therefore, be care- 

 fully guarded against. The study should be begun with 

 the vegetative form of the organisms ; the hanging-drop 

 preparation should, for this reason, always be made 

 from a perfectly fresh culture of the organism under 

 consideration before time has elapsed for spores to form. 



The simple detection of the presence or absence of 

 spore-formation can in many cases be made by other 

 methods. For example, many species of bacteria which 

 possess this property form spores most readily upon 

 media from which it is somewhat difficult for them to 

 obtain the necessary nourishment ; potatoes and agar-agar 

 that have become a little dry oifer very favorable con- 

 ditions, because of the limited area from which the 

 growing bacteria can draw their nutritive supplies, and 

 because of the free access which they have to oxygen, 

 for, their growth being on the surface, they are sur- 

 rounded by this gas unless means are taken to prevent 

 it. By the hanging-drop method, however, more than 

 this specific property may be determined. It is possible 

 not only to detect the stages and steps in the formation 

 14 



