42 THE STORY OF THE BACTERIA. 



for them in the early morning, there hung in 

 the place of the sausages a fiery effigy which 

 seemed to her more like the quondam spirits 

 of their mysterious ingredients than the unc- 

 tuous homely friend of the homeless boarder. 

 The explanation of this is now simple 

 enough without recourse to the supernatural ; 

 for it has been recently shown that this curious 

 light which various organic substances emit is 

 due, in many cases at least, to the enormous 

 numbers of certain kinds of bacteria which are 

 present on their surfaces, hard at work feeding 

 on the organic compounds which are present 

 and undergoing decay. Pure cultures of these 

 singular bacteria have been made and culti- 

 vated in considerable quantities. These bac- 

 terial masses, together with the tubes in which 

 they were growing, have been placed in a dark 

 room with an open watch beside them, and 

 bacterial masses, tubes, and all actually photo- 

 graphed by their own light, the pointers of the 

 watch showing distinctly the time of day. So 

 it would seem that this cousin of the will-o'-the- 

 wisp no doubt often mistaken for him is no 

 malevolent genius after all, but a quiet little 



