AIR 137 



organisms usually found being moulds and saprophytic bacteria. 

 The determination of the number of organisms is of greatest use 

 as a means of comparing methods of ventilation. 



Bacterial content of air. 



While numerous bacteriological examinations of air have 

 been carried out from time to time the data given mostly only 

 consist of the number of bacteria present. Such figures to be of 

 value must be carefully considered in the light of the precise 

 local conditions prevailing when they were obtained. The figures 

 mentioned below will, however, give a good idea of the bacterial 

 content of air under different conditions and in different places. 



Miquel found, as the average of six years' observations, 

 about 450 organisms per cubic metre in the air of the park at 

 Montsouris near Paris, while in a street of Paris he found the 

 average to be nearly 4000. 



Carnelley, Haldane and Anderson 1 carried out a series of 

 investigations in Scotland, chiefly in Dundee. They found that 

 the outside air in winter contained an average of 0*8 micro- 

 organisms (6 bacteria, 2 moulds) per litre. Some of their other 

 figures per litre of air were as follows, the results being the 

 averages of a large series of results. Elementary schools in 

 Dundee 152 bacteria, county board schools in Scotland 76, one- 

 roomed dwellings 60, two-roomed dwellings 46, better class 

 houses 9 bacteria. 



Classified in relation to cleanliness, etc., some of their results 

 are shown in the following table : 



Micro-organisms 

 per litre of air 



Elementary schools in 



Dundee with 



natural ventilation 



Elementary schools in 



Dundee with 

 natural ventilation 

 One-roomed 

 dwellings in 



Dundee 



Two-roomed 



dwellings in 



Dundee 



Cleaner than average ... 91 



Average ... ... ... 125 



Dirtier than average ... 198 



Opened over 20 years ... 311 



220 ... 150 



,, less than 20 years 38 



Cleaner than average ... 18 



Average 45 



Dirtier than average ... 93 



Cleaner than average ... 10 



Average 22 



Dirtier than average ... 69 



1 Philos. Transactions, 1887 B. 



