4 BACTERIA AND SOIL FERTILITY 



The theory of the spontaneous generation of mice, scorpions, 

 and maggots had been proven incorrect. But how about these 

 microscopic animalcules which had just been discovered? Surely 

 they could develop directly from dead material. For anyone 

 provided with this new instrument, the microscope, could easily 

 demonstrate for himself the spontaneous generation of micro- 

 scopic eels in vinegar or produce myriads of different and interest- 

 ing living creatures in simple infusions of hay or other organic 

 material. 



Needham evolved the theory that a force called "productive" 

 or "vegetative" existed which was responsible for the formation 

 of organized beings. The great naturalist, Buffon (1707-1788), 

 elaborated the theory that there were certain unchangeable parts 

 common to all living creatures. After death these ultimate con- 

 stituents were supposed to be set free and become very active, until 

 with one another and still other particles they gave rise to swarms 

 of microscopic creatures. 



Needham, a Catholic priest, in 1745 took decaying organic 

 matter and enclosed it in a vessel. This he placed upon hot ashes 

 to destroy any existing animalcules. On examining the contents 

 of the flasks he found microorganisms which were not there in the 

 beginning. Later in 1769 Spallanzani repeated the work, as he 

 felt that Needham had not exercised sufficient care and that the 

 organisms entered from the outside. The latter boiled the 

 material for one hour and kept it in hermetically sealed flasks. 

 He wrote: "I used hermetically sealed vessels. I kept them for 

 one hour in boiling water, and after opening and examining their 

 contents after a reasonable interval, I found not the slightest trace 

 of animalculse, though I had examined the infusion from nine- 

 teen dijfferent vessels." 



But the believers in the theory of spontaneous generation were 

 not convinced, for they claimed that the boiling altered the char- 

 acter of the infusion so that it was unable to produce life. Vol- 

 taire, with his characteristic satire, took up the fight at this point 

 and ridiculed the operations of the English clergy who had en- 

 gendered the eels in the gravy of boiled mutton, and he wittily 



