BACTERIA IN THE AIR IO/ 



the air. Frankland found that fewer germs were present 

 in the air in winter than in summer, and that when the 

 earth was covered with snow the number was greatly re- 

 duced. Miquel and Freudenreich have declared that the 

 number of atmospheric bacteria is greater in the morning 

 and evening between the hours of six and eight than during 

 the rest of the day. But we venture to express the hope 

 that such coincidental facts may not be exalted into prin- 

 ciples. 



There is no numerical standard for bacteria in the air as 

 there is in water. The open air possibly averages about 250 

 per cubic metre. On the seacoast this number would fall 

 to less than half; in houses and towns it would rise accord- 

 ing to circumstances, and frequently in dry weather reach 

 thousands per cubic metre. When it is remembered that 

 air possesses no pabulum for bacteria as do water and milk, it 

 will be understood that bacteria do not live in the air. They 

 are only driven by air-currents from one dry surface to 

 another. Hence the quality and quantity of air organisms 

 depend entirely upon environment and physical conditions. 

 In some researches which the writer made into the air of 

 workshops in Soho in 1896, it was instructive to observe 

 that fewer bacteria were isolated by Sedgwick's sugar-tube 

 in premises which appeared to the naked eye polluted in a 

 large degree than in other premises apparently less con- 

 taminated. In the workroom of a certain skin-curer the 

 air was densely impregnated with particles from the skin, 

 yet scarcely a single bacterium was isolated. In the polish- 

 ing-room of a well-known hat firm, in which the air appeared 

 ' to the naked eye to be pure, and in which there was ample 

 ventilation, there were found four or five species of sapro- 

 phytic bacteria. Quite recently Mr. S. R. Trotman, public 

 analyst for the city of Nottingham, estimated the bacterial 

 quality of the air of the streets of that town during " the 

 goose fair " held in the autumn. He used a modification 

 of Hesse's apparatus in which the gelatine is replaced by 



