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 !" 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. 



