THE LIFE HISTORY OF BACTERIA. 57 



the agency of other organisms; in other words, that life 

 could originate directly from dead matter. This view was 

 apparently substantiated by the fact that when an infusion 

 of wheat or barley was boiled in a closed flask for some 

 minutes and then set aside various bacteria would develop 

 in the liquid. The exposure to the temperature of boiling 

 w T ater was assumed to be sufficient to destroy all living 

 matter and consequently any new life that might subse- 

 quently develop must come from dead matter. Such was 

 the theory of spontaneous generation which, formulated 

 by Needham in 1747, persisted as a dominant idea for more 

 than 100 years. 



This theory existed because, in the first place, it was 

 not known that bacteria were to be found almost everywhere 

 in nature. In the second place, the existence of spores and 

 the remarkable degree of resistance which they possessed 

 was not dreamed of. The researches of Pasteur (1861) first 

 demonstrated the wide distribution of bacteria in the air and 

 elsewhere, and, above all, clearly proved the existence of 

 highly resistant forms of bacteria, the spores. A moderate 

 amount of boiling will kill all vegetating forms and some 

 feeble spores. The highly resistant spores are not destroyed 

 and hence subsequently germinate. The beginner in the lab- 

 oratory will invariably meet with instances of so-called 

 spontaneous generation whenever the culture media have 

 not been properly sterilized. The smallest of living beings, 

 like the highest forms of life, are always descended from 

 antecedents of their own kind. While it may not be true 

 to say that all life comes from the egg, it is true that " all 

 life comes from life." 



