OF CENTRAL LONDON RAILWAY 91 



By way of smiuuary, it may be said that Andrewes found that 

 micro-organisms were present in the air of the Central London 

 Eailway in a somewhat greater proportion (as 13 to 10) than in the 

 fresh air outside. The number was high in proportion to the 

 concentration of human traffic, being highest in carriages, platforms, 

 and lifts. The tube air does not compare unfavourably with that 

 known to exist in ordinary dweUing-rooms. No pathogenic germs 

 were discovered, though the number of organisms capable of growing 

 at body temperature was greater in the tube air than in the outside 

 air, and the number of organisms in the tube air was found generally 

 proportional to the degree of chemical contamination, but this rule 

 was subject to striking exceptions. It is evident that bacterial 

 contamination of air, though, as a rule, parallel to chemical con- 

 tamination, may yet vary quite independently as the result of special 

 conditions, such as air currents, which indicates that chemical 

 examination alone cannot always be taken as a trustworthy guide to 

 the contamination of air. 



The species of bacteria which Andrewes found in the railway 

 air were in the main identical with those occurring in fresh air, 

 and included Staplylococcus cereusjlavus et alius, Micrococcus candicans, 

 M. flavus, M. citreus, M. lactis, M. albicans tardissimus, Sarcina lutea, 

 S. fiava, S. alba, Bacilltis luteus, B. lactis innocuus, Streptothrix 

 Forsteri, S. chromogenes, S. albido-flava, Torula alba, and Saccharomyces 

 cerevisice. 



Inteppretation of Reports on Bacterial Content of Air 



In the present position of our knowledge of the bacteriology of 

 air, reports are only of comparative value. Mere numbers of sapro- 

 phytic bacteria in air are not of great service. Up to the present it 

 has not been possible to isolate pathogenic organisms, though such 

 must inevitably occur in air under certain circumstances, though even 

 then probably only in very small numbers. To detect pathogenic 

 organisms, it will probably be necessary to examine large volumes of 

 air, and by methods which will eliminate the common saprophytes. 

 The truth is that the foundations of our knowledge concerning the 

 bacterial flora of the air are only beginning to be laid, and until we 

 can detect, by bacteriological examination, organisms of disease, the 

 bacteriology of air can only be a subject of relative importance. 



