I3O ELEMENTS OF BIOLOGY. 



been produced spontaneously by the action of physical and 

 chemical forces upon the organic, but dead, materials held 

 in solution in the fluid. 



By another school, on the other hand, it is held that the 

 facts of the case may be explained upon the supposition 

 chat the air, all fluids exposed to the atmosphere, and 

 many solid bodies, are crowded with the microscopic 

 germs of minute living beings, animal or vegetable ; that 

 these germs may remain dormant for indefinite periods, 

 having the power of withstanding temperatures which would 

 be fatal to adult organisms ; but that they spring into active 

 life the moment the conditions which surround them are 

 favourable for their development. Such conditions are 

 presented by any fluid holding organic matter in solution ; 

 and it is believed that the living organisms which appear in 

 an organic infusion are merely developed from inconceiv- 

 ably minute germs, which fall into the infusion from the air, 

 or are contained in the fluid to begin with. 



It must be admitted that the above is to a certain extent 

 an hypothesis ; but it is not only supported by various ab- 

 stract considerations of great weight, but also rests upon a 

 firm if somewhat narrow basis of fact. Thus it has been 

 shown, beyond a question, that such germs are present in 

 the atmosphere, and in many other localities as well. We 

 may therefore safely assume as proved, that the air, most 

 fluids, and many organic and inorganic substances, contain 

 the germs of organisms which are capable of being developed 

 in active life, when once they are placed under suitable con- 

 ditions. We may regard this as proved wholly irrespective 

 of the belief that certain low organisms can be produced 

 spontaneously, without the presence of pre-existent germs. 

 Even if spontaneous generation were proved to be part of 

 the order of nature, the importance or validity of the fact 

 just stated would be in no way affected thereby. Even if 

 we were to admit the possible formation of living beings out 

 of dead matter, it would still remain certain that all nature 



