EDWARD ELSWORTH. 235 



ments of sand, broken fibres of plants, pollen, fine hairs, 

 the pulverized excreta of various domestic animals, 

 ashes, fibres of clothing and other fabrics, particles of 

 lime or plaster or soot, parts of seeds of plants, masses 

 and clusters of various kinds of micro organisms, and 

 partially ground up materials of kinds too numerous to 

 mention." 



Within this latter category I ought to include specifi- 

 cally a new form of dust which has made its appearance 

 in the city of New York since the advent of the elevated 

 railway system — viz., a vast amount of minute metallic 

 dust which has been liberated by the constant friction of 

 the car wheels over and against the rails, and the cease- 

 less jar of the whole iron structure. Oculists aver that 

 there has been a marked increase in the number of cases 

 of diseases of the eye since the building of these rail- 

 ways, and of external injury to the eyes, which may be 

 attributed directly to this cause. 



" The finer dust particles consist of fragments of fine 

 vegetable or animal fibres, such as cotten or woolen or 

 other light material, and of the greatest variety of micro 

 organisms either singly or in masses, such as bacteria 

 and mould spore." 



These latter forms are mostly invisible, except in a 

 beam of sunlight which streams into some darkened 

 room or corner. 



It is with these that Dr. Prudden chiefly deals, as 

 these insidious messengers of evil are the ones most 

 dangerous to human life. 



They are by no means confined to the highways and 

 market places, but are uninvited guests in all our 

 dwellings, and interior places of congregation. They 

 come in through many avenues, and fortunate is he who 

 studies best how to reduce their presence to the minimum. 



There is another danger from dust in some of our 

 dwellings which has not received the attention from 



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