DUST AND DISEASE. 309 



lution of caustic potash, the other sulphuric acid. " All the 

 bent tubes," says Dr. Bennett, " 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 contain- 

 ing 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 compe- 

 tence to do this. 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 the apparatus the very results which 

 Dr. Bennett has described — a retardation of the develop- 

 ment 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 his sifted air, and five with common air. In ten or 

 twelve days all the five had fungi in them ; while it re- 

 quired from four to nine months to develop fungi in the 

 others. In one case, moreover, even after this interval, no 

 fungi appeared. In a second series of experiments there 

 was a similar exception. In a third series of experiments 

 he abandoned the cork stoppers used in the first and second 

 series, and employed glass stoppers. 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 cases the prepared air was forced into the 

 infusion when it was boiling hot. Dr. Bennett made a 



