54 THE FLOATING-MATTER OF THE AIR. 



of the exposed liquid had changed from a pale sherry- 

 colour to a brown orange. On the 25th the tubes were 

 again examined, and found full of Bacteria. Two 

 months subsequent to this latter date the infusion, 

 diminished by evaporation, was found well charged 

 with Bacterial life. 



While this process of putrefaction was going on 

 outside, the tubes opening into the moteless air of the 

 case remained perfectly clear and void of life. 



The large chamber represented in fig. 2, and above 

 described, was the first operated on, and the liquid is 

 shown by the draughtsman as filling only a small portion 

 of the test-tubes. This smallness of volume is in part due 

 to evaporation. Test-tubes 1*2 inch wide and 9 inches 

 long were, in all subsequent experiments, nearly filled 

 with the infusions. Strong in the first instance, these 

 were sometimes kept until slow evaporation through the 

 bent tubes at the top of the case had reduced them to 

 one third or one fourth of their original volume. Each 

 experiment, therefore, was, in reality, a series of experi- 

 ments, extending over months, on infusions of different 

 strengths, the concluding ones of the series attaining a 

 very high degree of concentration. 



§ 4. Mutton-Infusion, 



A new case was constructed to contain six test-tubes* 

 It, like the others, had a front of glass, side windows, 

 and a back door. Its capacity was 857 cubic inches. It 

 was sealed up on the 21st of September, and found free 

 from floating matter on the 24th. The lean of mutton, 

 cut into small pieces, was digested, or soaked, for four 

 hours in water of a temperature of 120° F.^ The infu- 



* The temperature recommended by the supporters of sponta- 

 neous generation. 



