SPONTANEOUS GENERATION 19 



poet and physician, Redi, took the simple precaution of screening 

 the mouth of jars containing meat so that flies could not enter. 

 Flies were attracted by the odor and deposited their eggs on the 

 gauze, and it was from these that the so-called "worms" arose. 



The theory of the spontaneous generation of mice, scorpions, and 

 maggots had been proved untenable. But how about these micro- 

 scopic organisms ? They surely could develop directly from organic 

 material. For now anyone provided with this new instrument, the 

 microscope, could easily demonstrate for himself the spontaneous 

 generation of microscopic eels in vinegar, or produce myriads of 

 different and interesting living creatures in simple infusion of hay 

 or other organic material. 



Needham, a Catholic priest, evolved the theory that a force called 

 "productive" or "vegetative" existed which was responsible for 

 the formation of organized beings. The great naturalist, Buffon, 

 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 active, until, with 

 one another and still other particles, they gave rise to swarms of 

 microscopic creatures. 



Needham in 1745 took decaying organic matter and enclosed it in 

 a vessel; this he placed upon hot ashes to destroy any existing 

 animalculse. On examining the contents of the flasks he found micro- 

 organisms which he had not noted at first. Later (1769) , %>allanzani 

 repeated the work. He felt that Needham had not exercised suffi- 

 cient care and that the organisms had gotten in from the outside. 

 Accordingly he 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 nineteen different vessels." 



But the believers in the theory of abiogenesis were not convinced, 

 for they claimed that the boiling altered the character of the infusion 

 so that it was unable to produce life. Voltaire, with his characteristic 

 satire, took up the fight at this point and ridiculed the operations 

 of the English clergy " who had engendered the eels in the gravy of 

 boiled mutton," and he wittily remarks: "It is strange that men 

 should deny a creator and yet attribute to themselves the power of 

 creating eels." But this was a controversy to be settled not by 

 ridicule but by experimental evidence. 



Spallanzani answered this by cracking one of the flasks so that 

 air could enter. Decay soon set in. Even this was not sufficient to 

 overthrow a popular belief, for the claim was made that the sealing 

 of the flasks excluded the air, and air was essential to the generation 

 of these forms of life. This objection was answered by the work of 



