SPONTANEOUS GENERATION. 



299 



Were it our object, as it will be subsequently, to effec- 

 tually detain the dirt, we might coat that surface with 

 some sticky substance. Here, then, without ' torturing ' 

 the air in any way, we have found a means of ridding 



Fig. 24. 



it, or rather of enabling it to rid itself, of floating 

 matter. 



We have now to devise a means of testing the action 

 of such spontaneously purified air upon putrescible 

 infusions. Wooden chambers, or cases, are accordingly 



