1873—1877 21 



ponents and myself? Not only have I contradicted, proof in 

 hand, every one of their assertions, while they have never dared 

 to seriously contradict one of mine, but, for them, every cause 

 of error benefits their opinion. For me, affirming as I do 

 that there are no spontaneous fermentations, I am bound 

 to eliminate every cause of error, every perturbing influence, 

 I can maintain my results only by means of most irreproach- 

 able experiments; their opinions, on the contrary, profit by 

 every insufficient experiment and that is where they find their 

 support." 



Pasteur having been abruptly addressed by a colleague, 

 who remarked that there were yet many unexplained facts in 

 connection with fermentation, he answered by thus apostro- 

 phizing his adversaries — 



' What is then your idea of the progress of Science? 

 Science advances one step, then another, and then draws back 

 and meditates before taking a third. Does the impossibility 

 of taking that last step suppress the success acquired by the 

 two others ? Would you say to an infant who hesitated before 

 a third step, having ventured on two previous ones : ' Thy 

 former efforts are of no avail ; never shalt thou walk ' ? 



" You wish to upset what you call my theory, apparently in 

 order to defend another ; allow me to tell you by what signs these 

 theories are recognized : the characteristic of erroneous theories 

 is the impossibility of ever foreseeing new facts ; whenever such 

 a fact is discovered, those theories have to be grafted with 

 further hypotheses in order to account for them. True 

 theories, on the contrary, are the expression of actual facts 

 and are characterized by being able to predict new facts, 

 a natural consequence of those already known. In a word, 

 the characteristic of a true theory is its fruitfulness." 



"Science," said he again at the following sitting of the 

 Academy, "should not concern itself in any way with the 

 philosophical consequences of its discoveries. If through the 

 development of my experimental studies I come to demonstrate 

 that matter can organize itself of its own accord into a cell 

 or into a living being, I would come here to proclaim it with 

 the legitimate pride of an inventor conscious of having made 

 a great discovery, and I would add, if provoked to do so, ' All 

 the worse for those whose doctrines or systems do not fit in 

 with the truth of the natural facts.' 



' It was with similar pride that I defied my opponents to 



b 2 



