DUST AND DISEASE. 27 



On the other hand, is it impossible that disease germs 

 may exist free from dust ? 



Dr. Tyndall had thought " with the rest of the 

 world, that the dust of our air was in great part inor- 

 ganic and non-combustible." But from the " rest of the 

 world" must be excluded the majority of those who 

 have used a microscope or are acquainted with 

 the use of this instrument. Ought a lecturer to 

 excite the astonishment of his audience by trying to 

 convince them that until lately he was quite un- 

 acquainted with some things very generally known, and 

 when his hearers have become sufficiently interested 

 in this want of information on his part, relate as some 

 new discovery what he has happily to introduce to 

 their notice? Dr. Tyndall has discovered that the 

 little particles of cotton and hair and wool and 

 feathers and other organic substances which exist in 

 the air, can be destroyed by a red heat and converted 

 into smoke, which would not be the case had they 

 consisted of inorganic matter as he supposed before he 

 tried the experiment he proceeds to repeat.* 



their homes at Westminster. Whatever may be said against them, they 

 are evidently persons in rude health and more affected by the passive 

 organic and inorganic constituents of the dust than by its active disease- 

 producing germs. 



* Dr. Tyndall, after the publication of his lecture, announced in 

 the "Times," that Dr. Percy had discovered that the dust upon the 

 walls of the British Museum contained 50 per cent, of inorganic matter 

 this, in support of Dr. TyndalPs belief, that the dust of our air was in 

 great part inorganic and non-combustible. But Dr. Tyndall says nothing 

 about the nature of the remaining 50 per cent, of this dust. 



