452 



BACTERIOLOGY. 



give the number of org-anisms present in a cubic meter 

 (1000 liters) of air. 



On an average, it may be said that the country air 

 contains from 1 to 5 germs in 10 liters. Not infrequently 

 the air of private rooms and hospitals, especially after 

 sweeping, may contain 20 to 50 thousand organisms. In 

 the absence of currents of air these suspended germs rapidly 

 settle and are not removed by ordinary ventilation. Dry 

 sweeping and dusting should, therefore, be avoided, especially 

 ' in rooms which are occupied by persons afflictfed with con- 

 sumpton or with other infectious diseases. 



The vast majority of the bacteria present in the air are 

 harmless saprophytes. Pathogenic bacteria are present, 

 relatively, in very small numbers and hence their detection 

 is extremely difficult. The pus-producing micrococci have 

 been isolated direct from the air. The tubercle bacillus 

 enters the body through the air and yet direct examinations, 

 for the reasons given, have thus far been negative. It has 

 been detected, however, in the dust of rooms, — that is to 

 say in the sediment deposited from the air. 



Method of analysis. — It was pointed out in connection 

 with the analysis of water (p. 437) that the number of bac- 

 teria present could not be determined absolutely. The same 



