162 FKAGMENTS OF SCIENCE. 



U-tubes, the one containing a solution of caustic potash, 

 the other sulphuric acid. ' All the bent tubes were 

 filled with fragments of pumice-stone to break up the 

 air, so as to prevent the possibility of any germs passing 

 through in the centre of bubbles.' The air also passed 

 through a Liebig's bulb containing sulphuric acid, and 

 also through a bulb containing gun-cotton. 



It was only natural for Dr. Bennett to believe that 

 his ' bent tubes ' entirely cut off the germs. Previous 

 to the observations just referred to, I also believed in 

 their efficacy. But these observations destroy any such 

 notion. The gun-cotton, moreover, will fail to arrest 

 the whole of the floating matter, unless it is tightly 

 packed, and there is no indication in Dr. Bennett's 

 memoir that it was so packed. On the whole, I should 

 infer, from the mere inspection of Dr. Bennett's appa- 

 ratus, the very results which he has described a retar- 

 dation of the development of life, a total absence of it 

 in some cases, and its presence in others. 



In his first series of experiments, eight flasks were 

 fed with sifted air, and five with common air. In 

 ten or twelve days all the five had fungi in them ; 

 whilst it required from four to nine months to develop 

 fungi in the others. In one of the eight, moreover, 

 even after this interval no fungi appeared. In a second 

 series of experiments there was a similar exception. In 

 a third series the cork stoppers used in the first and 

 second series were abandoned, and glass stoppers em- 

 ployed. Flasks containing decoctions of tea, beef, and 

 hay were filled with common air, and other flasks with 

 sifted air. In every one of the former fungi appeared and 

 in not one of the latter. These experiments simply ruin 

 the doctrine that Dr. Bennett finally espouses. 



In all these negative cases, the prepared air was 

 forced into the infusion when it was boiling hot. Dr. 



