APHORISMS AND REFLECTIONS 85 



dispensed with altogether, and perfectly free access 

 left between the exterior air and that in the experi- 

 mental flask. If the neck of the flask is drawn out 

 into a tube and bent downwards ; and if, after 

 the contained fluid has been carefully boiled, the 

 tube is heated sufficiently to destroy any germs 

 which may be present in the air which enters 

 as the fluid cools, the apparatus may be left to itself 

 for any time and no life will appear in the fluid. 

 The reason is plain. Although there is free com- 

 munication between the atmosphere laden with 

 germs and the germless air in the flask, contact 

 between the two takes place only in the tube ; and 

 as the germs cannot fall upwards, and there are nc 

 currents, they never reach the interior of the flask. 

 But if the tube be broken short off where it proceeds 

 from the flask, and free access be thus given to 

 germs falling vertically out of the air, the fluid, 

 which has remained clear and desert for months, 

 becomes, in a few days, turbid and full of life. 



In autumn it is not uncommon to see flies 

 motionless upon a window-pane, with a sort oi 

 magic circle, in white, drawn round them. On 

 microscopic examination, the magic circle is found 

 to consist of innumerable spores, which have been 

 thrown off in all directions by a minute fungus 

 called Etupnsa mitscre, the spore-forming filaments 

 of which stand out like a pile of velvet from the 

 body of the fly. These spore-forming filaments 

 are connected with others which fill the interior 

 of the fly's body like so much fine wool, having 

 eaten away and destroyed the creature's viscera. 

 This is the full-grown condition of the Empusa. 

 If traced back to its earliest stages, in flies which 

 are still active, and to all appearance healthy, it 

 is found to exist in the form of minute corpuscles 



