PHENOMENA OF LIFE 9 



verity of the theory of spontaneous generation. Redi proved con- 

 clusively that maggots never rise de now from decaying flesh, as 

 had been believed up to his time. He exposed meat in three jars 

 under diverse conditions; one was left open, the second was 

 covered with gauze, and the third was covered with parchment. 

 The meat decayed in all of the jars, but maggots appeared only 

 in the meat in the one which had been left entirely uncovered. 

 Flies were attracted by the decaying meat in the second jar, but, 

 being unable to enter, laid their eggs on the gauze, where they 

 were found by Redi. No eggs were laid on the third jar, for the 

 parchment did not allow odors to escape. By these and other 

 experiments the theory of spontaneous generation fell into dis- 

 repute, but many of its adherents still maintained that even 

 though some animals might not originate spontaneously, that 

 fact did not preclude the possibility of others doing so. 



Such dissenters made their last stand when the microscope 

 revealed the swarms of minute animals which had been previously 

 unknown. In one of their experiments hay was boiled in water 

 until all the life had been killed; the liquid was then filtered off 

 and placed in a tightly stoppered bottle. The subsequent 

 appearance of a scum of living organisms in such infusions con- 

 vinced them that life had arisen spontaneously. In 1775, 

 Spallanzani proved that when proper precautions were observed 

 no life developed in a culture of this kind. He prevented the 

 entrance of air into the vessels containing the nutrient solution 

 by hermetically sealing the slender necks of his flasks in flame. 

 The flasks were then placed in boiling water for three quarters 

 of an hour, all germs contained in them being destroyed. No 

 life appeared in nutrient fluids thus treated. Despite this 

 demonstration the question continued to be agitated for many 

 years, and it was not until the time of Pasteur (1864) and Tyndall 

 (1876) that the old theory of spontaneous generation was com- 

 pletely overthrown. 



At the present time we are able to affirm that no living organ- 

 ism is known to originate except from some other preexisting 



