TEE LIFE-WORK OF PASTEUR, 239 



mineral matters tliat can feed the plant, as I have directly demon- 

 strated. You have, moreover, not carefully examined the surface of 

 the chips with the microscope. If you had, you would have seen the 

 little articles of the Mycoderma aceti, sometimes joined into an ex- 

 tremely thin pellicle that may be lifted off. If you will send me some 

 chips from the factory at Munich, selected by yourself in the presence 

 of its director, I will, after drying them quickly in a stove, show the 

 mycoderm on their surface to a committee of the Academy charged 

 with the determination of this debate." Liebig did not accept the 

 challenge, but the question involved has been decided. 



The experiments in fermentation led by natural steps to the debate 

 on spontaneous generation, in which Pasteur was destined to settle 

 a question that had interested men ever since they lived. The 

 theory that life originates spontaneously from dead matter had strong 

 advocates, among the most earnest of whom was M. Pouchet. He 

 made a very clear presentment of the question at issue, saying : " The 

 adversaries of spontaneous generation assume that the germs of micro- 

 scopic beings exist in the air and are carried by it to considerable dis- 

 tances. Well ! what will they say if I succeed in producing a genera- 

 tion of organized beings after an artificial air has been substituted for 

 that of the atmosphere ? " Then he proceeded with an experiment in 

 which all his materials and vessels seemed to have been cleansed of all 

 germs that might possibly have existed in them. In eight days 

 a mold appeared in the infusion, which had been put boiling-hot into 

 the boiling-hot medium. " Where did the mold come from," asked M. 

 Pouchet, triumphantly, "if it was not spontaneously developed?" 

 "Yes," said M. Pasteur, in the presence of an enthusiastic audience, for 

 Paris had become greatly excited on the subject, " the experiment has 

 been performed in an irreproachable manner as to all the points that 

 have attracted the attention of the author ; but I will show that there 

 is one cause of error that M. Pouchet has not perceived, that he has 

 not thought of, and no one else has thought of, which makes his experi- 

 ment wholly illusory. He used mercury in his tub, without purifying 

 it, and I will show that that was capable of collecting dust from the 

 air and introducing it to his apparatus." Then he let abeam of light 

 into the darkened room, and showed the air full of floating dust. 

 He showed that the mercury had been exposed to atmospheric dust 

 ever since it came from the mine, and was so impregnated and covered 

 with it as to be liable to soil everything with which it came in contact. 

 He instituted experiments similar to those of M. Pouchet, but with all 

 the causes of error that had escaped him removed, and no life appeared. 

 The debate, which continued through many months, and was diversi- 

 fied by a variety of experiments and counter-experiments, was marked 

 by a number of dramatic passages and drew the attention of the world. 

 M. Pasteur detected a flaw in every one of M. Pouchet's successful ex- 

 periments, and followed each one with a more exact experiment of his 



