DUST AND ITS DANGERS. 33 



in the air before and after sweeping, if the 

 rooms are not frequently carefully and properly 

 swept and dusted. Thus in a carpeted living- 

 room in a tenement on loth Avenue, 75 bacteria 

 and i mould settled on to the surface of the 

 exposed plate in five minutes before sweeping. 

 When the room was still, immediately after 

 sweeping, a similar experiment showed over 

 2,700 bacteria and 6 moulds. 



Carnelly found in hospital wards in Dundee 

 in the afternoons from 10 to 20 bacteria in 10 

 litres of air. Neumann found after sweeping 

 from 80 to 140 bacteria, and later in the day 

 from 4 to 10 in 10 litres. On the other hand, 

 Carnelly found in houses which are denomin- 

 ated clean, 180 bacteria in 10 litres of air, 

 while in very dirty houses there were over 

 900. In dirty school-rooms, with the so-called 

 natural ventilation, he found in the same vol- 

 ume of air nearly, 2,000 living bacteria, while 

 in mechanically ventilated schools there were 

 from 30 to 300. 



The writer has found as the result of 23 

 analyses of the air of various laboratories, 

 lecture-rooms, and hall-ways, at the College of 



