SPONTANEOUS GENERATION 329 



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

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

 sions. Wooden chambers, or cases, are accordingly con- 

 structed, having glass fronts, side -windows, and back- 

 doors. Through the bottoms of the chambers test-tubes 

 pass air-tight; their open ends, for about one-fifth of the 

 length of the tubes, being within the chambers. Provis- 

 ion is made for a free connection through sinuous chan- 

 nels between the inner and the outer air. Through such 

 channels, though open, no dust will reach the chamber. 

 The top of each chamber is perforated by a circular hole 

 two inches in diameter, closed air-tight by a sheet of india- 

 rubber. This is pierced in the middle by a pin, and 

 through the pin-hole is pushed the shank of a long pipette 

 ending above in a small funnel. The shank also passes 

 through a stuffing-box of cotton-wool moistened with glyc- 

 erine; so that, tightly clasped by the rubber and wool, 

 the pipette is not likely in its motions up and down to 

 carry any dust into the chamber. The illustration (page 

 330) shows a chamber, with six test-tubes, its side-win- 

 dows w w, its pipette p C, and its sinuous channels a b 

 which connect the air of the chamber with the outer air. 



The chamber is carefully closed and permitted to re- 

 main quiet for two or three days. Examined at the begin- 

 ning by a beam sent through its windows, the air is found 

 laden with floating matter, which in three days has wholly 

 disappeared. To prevent its ever rising again, the internal 

 surface of the chamber was at the outset coated with glyc- 

 erine. The fresh but putrescible liquid is introduced into 



