386 LOUIS PASTEUR 



repeat, is formed the septic dust, and we are able to under- 

 stand what has before seemed so obscure; we can see how 

 putrescible fluids can be inoculated by the dust of the air, 

 and how it is that putrid diseases are permanent in the 

 world. 



The Academy will permit me, before leaving these in- 

 teresting results, to refer to one of their main theoretical 

 consequences. At the very beginning of these researches, 

 for they reveal an entirely new field, what must be insistently 

 demanded? The absolute proof that there actually exist 

 transmissible, contagious, infectious diseases of which the 

 cause lies essentially and solely in the presence of micro- 

 scopic organisms. The proof that for at least some dis- 

 eases, the conception of spontaneous virulence must be for- 

 ever abandoned as well as the idea of contagion and an 

 infectious element suddenly originating in the bodies of 

 men or animals and able to originate diseases which propa- 

 gate themselves under identical forms: and all of those 

 opinions fatal to medical progress, which have given rise 

 to the gratuitous hypotheses of spontaneous generation, 

 of albuminoid ferments, of hemiorganisms, of archebiosis, 

 and many other conceptions without the least basis in obser- 

 vation. What is to be sought for in this instance is the proof 

 that along with our vibrio there does not exist an independent 

 virulence belonging to the surrounding fluids or solids, 

 in short that the vibrio is not merely an epiphenomenon 

 of the disease of which it is the obligatory accompaniment. 

 What then do we see, in the results that I have just brought 

 out? A septic fluid, taken at the moment that the vibrios 

 are not yet changed into germs, loses its virulence com- 

 pletely upon simple exposure to the air, but preserves this 

 virulence, although exposed to air on the simple condition 

 of being in a thick layer for some hours. In the first 

 case, the virulence once lost by exposure to air, the liquid 

 is incapable of taking it on again upon cultivation: but, 

 in the second case, it preserves its virulence and can propa- 

 gate, even after exposure to air. It is impossible, then, to 

 assert that there is a separate virulent substance, either 

 fluid or solid, existing, apart from the adult vibrio or its 

 germ. Nor can it be supposed that there is a virus which 







