STUDIES IN ANIMAL LIFE. 19 



tides inward, the cilia energetically beat them back 

 if they attempt to enter. Fatal results would ensue 

 if this were not so. Our air-passages would no 

 longer protect the lungs from particles of sand, coal- 

 dust, and filings flying about the atmosphere ; on 

 the contrary, the lashing hairs which cover the sur- 

 face of these passages would catch up every parti- 

 cle, and drive it onward into the lungs. Fortunate- 

 ly for us, the direction of the cilia is reversed, and 

 they act as vigilant janitors, driving back all va- 

 grant particles with a stern " No admittance, even 

 on business 1" In vain does the whirlwind dash a 

 column of dust in our faces — ^in vain does the air, 

 darkened with coal-dust, impetuously rush up the 

 nostrils ; the air is allowed to pass on, but the dust 

 is inexorably driven back. Were it not so, how 

 could miners, millers, iron-workers, and all the mod- 

 ern Tubal Cains contrive to live in their loaded 

 atmospheres? In a week their lungs would be 

 choked up. 



Perhaps you will tell me that this is the case — 

 that manufacturers of iron and steel are very subject 

 to consumption, and that there is a peculiar discol- 

 oration of the lungs which has often been observed 

 in coal-miners examined after death. 



Not being a physican, and not intending to trouble 

 you with medical questions, I must still place be- 

 fore you three considerations, which will show how 

 untenable this notion is. First, although consump- 

 tion may be frequent among the Sheffield workmen, 



