BACTERIA IN SEWER AIR 83 



give up germs to the subsoil air, but they are satisfied that the air 

 of sewers themselves does not play any part in the conveyance of 

 the typhoid bacillus.* 



In passing, mention may be made of some interesting observations 

 recorded by Mr S. G. Shattock on the effect of sewer air upon the 

 toxicity of lowly virulent bacilli of diphtheria. Some direct relation- 

 ship, it has been surmised, exists between breathing sewer air and 

 "catching" diphtlieria. Clearly, it cannot be that the sewer air 

 contains the bacillus. But some have supposed that the sewer air 

 has had a detrimental effect by increasing the virulent properties of 

 bacilli already in the human tissues. Two cultivations of lowly 

 virulent B. diphtherim were therefore grown by Mr Shattock in flasks 

 upon a favourable medium over which was drawn sewer air. This 

 was continued for two months in the one case, and five weeks in the 

 other. Yet no increased virulence was secured.f Such experiments 

 require ample confirmation, but even now it may be said that sewer 

 air does not necessarily have a favouring influence upon the virulence 

 of the bacilli of diphtheria. Such experiments do not affect the 

 contrary question of the possibility of sewer air depressing the vitality 

 of the individual, and so allowing even lowly virulent bacilli to do 

 mischief. Of such depression caused by breathing sewer air there 

 is clinical proof, and although sewer-men do not appear to be affected, 

 persons freshly breathing sewer air may be. 



It should be noted that the bacilli of diphtheria are capable of 

 lengthened survival outside the body, and are readily disseminated 

 by very feeble air - currents. The condition necessary for their 

 existence outside the body for any period above two or three days 

 is moisture. Dried diptheria bacilli soon lose their vitality. It is 

 possible, owing to this fact, that the disease is not as commonly con- 

 veyed by air as, for example, tubercle. 



3. The Influence of Gravity upon bacteria in the air may be 

 observed in various ways, in addition to its action within a hmited 

 area like a sewer or a room. Miquel found in some investigations 

 in Paris that, whereas on the Kue de Eivoli 750 germs were present 

 in a cubic metre, yet at the summit of the Pantheon only 28 were 

 found in the same quantity of air. Frankland found that air at the 

 top of Primrose Hill contained 9 organisms per ten litres, and air 

 at the bottom 24. On the spire of Norwich Cathedral (310 feet), 

 ten litres of air yielded 7 organisms, on the tower (180 feet) 9, and 

 on the ground 18. At the level of the golden gallery of St Paul's 

 Cathedral he found in every ten litres 11 bacteria, at the stone gallery 

 34, and in St Paul's Churchyard 70. As Tyndall has pointed out, 



* Report to the London County Gouncil on the Result of Investigation on the Micro- 

 organisms of Sewage, by J. Parry Laws and F. W. Andrewes, 1894, p. 14. 

 t Pathological Society of London, Transactions, 1897. 



