VITALITY OF PUTEEFACTITE OEGANISMS. 169 



Fig. 16. 



§ 12. Infusions protected by Glass Shades 

 containing Calcined Air. 



I have already described this mode of experiment.' 

 The shades stood upon circular plates of wood, each 

 supported on a tripod (see fig. 16). Under each shade 

 were two upright rods of stout copper wire, and stretch- 

 ing from rod to rod was a spiral (p) of platinum wire. 

 The copper wires passed 

 through the slab of wood, 

 their free ends being in 

 the air. The rim of each 

 shade was surrounded by a 

 collar of tin attached by 

 wax to the slab, with a 

 space of about half an 

 inch between the collar 

 and the glass. After the 

 introduction of the infu- 

 sions and the mounting of 

 the shades, this annular 

 space was packed with 

 cotton-wool. The aim 

 here was to destroy the 

 floating matter of the air by the incandescent pla- 

 tinum spiral. The air heated by the spiral would of 

 course expand, passing outwards through the cotton- 

 wool, while the air re-entering, on the cooling of 

 the shade, would be duly sifted by the wool. In my 

 former experiments five minutes' incandescence sufficed 

 to render the air absolutely inoperative on infusions 

 exposed to its action. 



In the present experiments the period of incan- 

 ' Phil. Trans, vol. clxvi, p. 50. 



