BACTERIA IN THE AIR 1 05 



wet, the surrounding air will contain no bacilli of tubercle. 

 But when in the course of time the sputum dries, then the 

 least current of air will at once infect itself with the dried 

 spores and bacilli. 



Typhoid Fever, too, occupies the same position. Only 

 when the excrement dries can the contained bacteria infect 

 the air. It is of course well known that the common chan- 

 nel of infection in typhoid fever is not the air, whereas 

 the reverse holds true of tuberculosis. The writer recently 

 obtained some virulent typhoid excrement, and placed it 

 in a shallow glass vessel under a bell-jar, with similar vessels 

 of sterilised milk and of water, all at blood-heat. So long 

 as the excrement remained moist, even though it soon lost 

 its more or less fluid consistence, the milk and water re- 

 mained uninfected. But when the excrement was com- 

 pletely dried it required but a few hours to reveal typhoid 

 bacilli in the more absorptive fluid, milk, and at a later 

 stage the water also showed clear signs of pollution. This 

 evidence points in the same direction as that which has 

 gone before. If the excrement of patients suffering from 

 typhoid dries, the air will become infected; if, on the other 

 hand, it passes in a moist state into the sewer, even though 

 untreated with disinfectants, all will be well as regards the 

 surrounding air.- 



Before passing on to consider other matters concerning 

 organisms in the air, we may draw attention to some in- 

 teresting observations recorded by Mr. S. G. Shattock l on 

 the negative action of sewer air in raising the toxicity of 

 lowly virulent bacilli of diphtheria. Some direct relation- 

 ship, it has been surmised, exists between breathing sewer 

 air and " catching " diphtheria. Clearly it cannot be that 

 the sewer air contains the bacillus. But some have sup- 

 posed that the sewer air has had a detrimental effect by 

 increasing the virulent properties of bacilli already in the 



1 Pathological Society of London, Transactions, 1897. 



