SPONTANEOUS GENERATION. 35 



cold water, so as to make an organic infusion, and if this in- 

 fusion be exposed for a sufficient length of time to the air, 

 the following series of changes is usually observed : 



1. At the end of a longer or shorter time, there forms upon 

 the surface of the infusion a thin scum, or pellicle, which, 

 when examined microscopically, is found to consist of an in- 

 calculable number of extremely minute molecules. 



2. In the next stage these molecules appear, many of them, 

 to have melted together in twos and threes to form short fila- 

 ments, called " bacteria," which become longer by the appo- 

 sition of fresh molecules at their extremities, or by uniting 

 with one another, when they are termed " vibriones." Both 

 the bacteria and the vibrios now exhibit a vibratile or serpen- 

 tine movement through the surrounding fluid. 



3. After a varying period, the bacteria and vibrios become 

 motionless, and disintegrate so as to produce again a finely 

 molecular pellicle. 



4. Little spherical bodies now appear, each of which is 

 provided with a vibratile cilium with which it moves actively 

 through the infusion. (Monas lens.) 



5. Varied forms of ciliated Infusoria some which possess 

 a mouth and are otherwise highly organised make their 

 appearance in the fluid. 



The above is the general sequence of the phenomena which 

 have been observed, and the following are the two theories 

 which have been advanced to account for them : 



a. By the advocates of spontaneous generation, or " Hetero- 

 geny," it is affirmed that the Infusoria, which finally appear in 

 the infusion, are produced spontaneously out of the molecular 

 pellicle, the molecules of which are also of spontaneous origin, 

 and are not derived from any pre-existing germs. 



b. By the " panspermists," or the opponents of spontaneous 

 generation, it is alleged, on the other hand, that the produc- 

 tion of Bacteria, Vibrios, Monads, and Infusoria, in organic 

 infusions, is due simply to the fact that the atmosphere, 

 and probably the fluid itself, is charged with innumerable 

 germs too minute, perhaps, to be always detectable by the 

 microscope which, obtaining access to the fluid, and finding 

 there favourable conditions, are developed into living beings. 



A large number of elaborate experiments have been carried 

 out to prove that atmospheric air is absolutely necessary for 

 the production of these living beings, and that if the air be 

 properly purified by passage through destructive chemical 

 reagents, no such organisms will be produced, provided that 

 the infusion have been previously boiled. As the results of 



