SPONTANEOUS GENERATION. 37 



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 favour 

 able 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 

 all these experimental trials have hitherto proved more or less 

 contradictory, it is unnecessary to enter into the question 

 further, and it will be sufficient to indicate the following general 

 considerations : — 



a. The primary molecules which appear in the fluid are ex- 

 tremely minute, and if they are developed from germs, these 

 may. be so small as to elude any power of the microscope yet 

 known to us. As they subsequently become converted into 

 bacteria and vibrios, and as there can be little dispute as to 

 these being truly living organisms, we are obliged to believe 

 that they must have had some definite origin. It appears, 

 however, to be hardly philosophical to assume that they form 

 themselves out of the inorganic materials of the infusion; since 

 this implies the sudden appearance, or creation, of new force, 

 for which there seems to be no means of accounting. 



