ON DUST AND DISEASE. 161 



kinds passed with freedom through the plug of cotton- 

 wool ; hence the thing whose removal by the cotton- 

 wool rendered the gas impotent, could not itself have 

 been matter in the gaseous condition. It at once 

 occurred to me that the retina, protected as it was, in 

 these experiments, from all extraneous light, might be 

 converted into a new and powerful instrument of demon- 

 stration in relation to the germ theory. 



But the observations also revealed the danger in- 

 curred in experiments of this nature ; showing that 

 without an amount of care far beyond that hitherto 

 bestowed upon them, such experiments left the door 

 open to errors of the gravest description. It was 

 especially manifest that the chemical method employed 

 by Schultze in his experiments, and so often resorted 

 to since, might lead to the most erroneous conse- 

 quences ; that neither acids nor alkalies had the power 

 of rapid destruction hitherto ascribed to them. In 

 short, the employment of the luminous beam rendered 

 evident the cause of success in experiments rigidly con- 

 ducted like those of Pasteur ; while it made equally 

 evident the certainty of failure in experiments less 

 severely carried out. 



Dr. Bennett's Experiments. 



But I do not wish to leave an assertion of this kind 

 without illustration. Take, then, the well-conceived 

 experiments of Dr. Hughes Bennett, described before 

 the Royal Society of Surgeons in Edinburgh on January 

 17, 1868. l Into flasks containing decoctions of liquor- 

 ice-root, hay, or tea, Dr. Bennett, by an ingenious 

 method, forced air. The air was driven through twx> 



1 'British Medical Journal,' 13, pt. ii. 1868. 

 VOL. I. M 



