108 THE LIFE OF PASTEUR 



prepared to-day. To-morrow it will contain animalculse, little 

 infusories, or flakes of mouldiness. 



" I place a portion of that infusion into a flask with a long 

 neck, like this one. Suppose I boil the liquid and leave it to 

 cool. After a few days, mouldiness or animalcule will develop 

 in the liquid. By boiling, I destroyed any germs contained in 

 the liquid or against the glass ; but that infusion being again 

 in contact with air, it becomes altered, as all infusions do. 

 Now suppose I repeat this experiment, but that, before boiling 

 the liquid, I draw (by means of an enameller's lamp) the neck 

 of the flask into a point, leaving, however, its extremity open. 

 This being done, I boil the liquid in the flask, and leave it to 

 cool. Now the liquid of this second flask will remain pure not 

 only two days, a month, a year, but three or four years — for 

 the experiment I am telling you about is already four years old, 

 and the liquid remains as limpid as distilled water. What dif- 

 ference is there, then, between those two vases? They contain 

 the same liquid, they both contain air, both are open ! Why 

 does one decay and the other remain pure? The only dif- 

 ference between them is this : in the first case, the dusts sus- 

 pended in air and their germs can fall into the neck of the 

 flask and arrive into contact with the liquid, where they find 

 appropriate food and develop ; thence microscopic beings. In 

 the second flask, on the contrary, it is impossible, or at least 

 extremely difficult, unless air is violently shaken, that dusts 

 suspended in air should enter the vase ; they fall on its curved 

 neck. When air goes in and out of the vase through diffusions 

 or variations of temperature, the latter never being sudden, the 

 air comes in slowly enough to drop the dusts and germs that 

 it carries at the opening of the neck or in the first curves. 



"This experiment is full of instruction; for this must be 

 noted, that everything in air save its dusts can easily enter the 

 vase and come into contact with the liquid. Imagine what you 

 choose in the air — electricity, magnetism, ozone, unknown 

 forces even, all can reach the infusion. Only one thing cannot 

 enter easily, and that is dust, suspended in air. And the proof 

 of this is that if I shake the vase violently two or three times, 

 in a few days it contains animalcule or mouldiness. Why? 

 because air has come in violently enough to carry dust with it. 



" And, therefore, gentlemen, I could point to that liquid and 

 say to you, I have taken my drop of water from the immensity of 

 creation, and I have taken it full of the elements appropriated 



