60 THE FLOATING-MATTER OF THE AIR. 



actively charged tubes were in part crowned by beautiful 

 tufts of Penicillium glaucum.^ This expanded gra- 

 dually until it covered the entire surface with a thick 

 tough layer, which must have seriously intercepted the 

 oxygen necessary to the Bacterial life. The Bacteria 

 lost their translatory power, fell to the bottom, and left 

 the liquid between them and the superficial layer clear. 



Another difference, pointing to dififerences in the 

 unseen life of the air, was shown by these tubes. The 

 turbidity of the two mould-crowned ones was colourless, 

 exhibiting a grey hue. The third tube, the middle one 

 of the three, contained a bright yellow-green pigment, 

 and on its surface no trace of mould was to be seen. 

 It never cleared, but maintained its turbidity and its 

 Bacterial life for months after the other tubes had ceased 

 to show either. It cannot be doubted that the mould- 

 spores had fallen into this tube also, but in the fight for 

 existence the colour-producing Bacteria had the upper 

 hand. Six other tubes, similarly exposed, showed the 

 grey muddiness : all of them became thickly covered 

 with mould, under which the Bacteria died or passed 

 into a quiescent state, fell to the bottom, and left the 

 liquid clear. 



Up to the I3th of October the purity of the six 

 protected tubes remained unimpaired. 



Here a complementary experiment was made. It 

 remained to be proved that those long-dormant clear 

 infusions had undergone no change which interfered 

 with their ability to develop and maintain life. On the 

 13th of October, therefore, the small panel was removed 

 from the back of one of the cases, and with three new 

 pipettes specimens were taken from the three tubes 

 within it. The closest search revealed no living thing. 

 • Ordinary mould. 



