34 DUST AND ITS DANGERS. 



Physicians and Surgeons in New York, under 

 the ordinary conditions of occupation by con- 

 siderable numbers of students during 1 March and 

 April, 1890, that the average number of bacteria 

 in 10 litres was n and of moulds 14. 



The average number of germs in various 

 hospitals and dispensaries in New York during 

 the same period in 10 litres of air, (19 analyses) 

 was bacteria 127, moulds 25. 



We thus see that the number of living germs 

 in a given volume of in-doors air varies greatly 

 in different places and under different con- 

 ditions. We see that the temporary freeing of 

 the in-doors air from germs can be accomplished 

 by simply closing the rooms and keeping the 

 contained air still when within one or two 

 hours nearly all dust and most of the bacteria 

 will have settled to the lowest resting-place. 

 Whether the air shall be permanently rid of its 

 living or inert dust particles or not, will of 

 course depend upon the measures which are 

 resorted to in the familiar performances of 

 sweeping and dusting, of which more by and by. 



A good many of these facts which have been 

 just set down in regard to dust, are embodied 



