THE BEGINNINGS OF LIFE. 277 



other hand, are just as closely related to Leptothrix^ 

 and through these to the lower kinds of Fungi known 

 as c moulds.' Leptotkrix filaments are also, for the 

 most part, quite motionless, and are often not much 

 thicker than Vibriones. They may be either straight or 

 undulating in outline, and perfectly plain or marked 

 by minute segmentations after the fashion of the 

 larger fungus filaments into which they sometimes 

 develop. In addition to the larger organisms already 

 mentioned, there are other rarer forms, belonging to 

 the genus Spirillum^ characterized by the most active 

 movements, and in which the body is thread-like 

 though twisted into the form of a helix or spiral. 



It will be easily understood that the nature of the 

 pellicle must vary very much in different solutions, 

 according to the varying proportions in which these 

 several kinds of organic units and organisms enter into 

 its composition. All are agreed, however, that plastide 

 specks and the more minute and simpler organisms 

 are the first things to make their appearance in pre- 

 viously homogeneous solutions ; and that, later, whilst 

 these increase in number, there may gradually appear 

 Vlbr tones ^ Leptothrix filaments, Fungus-spores, or some of 

 the other lower forms of life. A very large propor- 

 tion of the organisms met with in organic infusions 

 are Bacteria., and their life and active movements 

 continue for a longer or a shorter period, the duration 

 of which is altogether uncertain. After a time, at 

 all events, they gradually tend to accumulate at the 



