PUTEEFACTION AND INFECTION. 61 



Tlie air of the laboratoiy being permitted to diffuse 

 freely into the case, on the day after the removal of the 

 panel the test-beam showed the case to be charged with 

 floating matter. 



The access of this 'matter was the only condition 

 necessary to the production of life ; for on the 11 th all 

 the tubes were muddy and aiv arming with Bacteria. 



A similar experiment, subsequently made, revealed 

 some of the snares and pitfalls which await an in- 

 cautious worker. The chamber already referred to 

 as containing six tubes, filled with turnip-juice, pre- 

 served the infusion clear for a month. On the 21st 

 of October the back door of the chamber was opened, 

 and specimens of the clear infusion were taken out 

 for examination by the microscope. The first tube 

 examined showed no signs of life. This result was 

 expected. Picking up another pipette, I took a 

 sample from the second tube. Here, to my astonish- 

 ment, the exhibition of life was monstrously copious. 

 There were numerous globular organisms, which re- 

 volved, rotated, and quivered in the most extraor- 

 dinary manner. There were also numbers of lively 

 Bacteria darting to and fro. An experimenter who 

 ponders his work and reaches his conclusions slowly, 

 cannot immediately relinquish them : and in the pre- 

 sent instance some time was required to convince me 

 that no mistake had been made. I could find none, 

 and was prepared to accept tlie conclusion that in the 

 boiled infusion, despite its clearness, life had appeared. 



But why, in the protected turnip-infusion, which 

 had been examined on the 13th of October, could no 

 trace of life be found ? In this case perfect transparency 

 was accompanied by an utter absence of life. The 

 selfsame action upon light that enabled the Bacteria 

 to show themselves in the microscope must, one would 



