CHAPTEK VII 



THE MICROBES OF THE AIR 



'THE solid matter floating in the atmosphere is 

 every day becoming of greater and greater interest 

 as we are gradually realising the important part it 

 plays in the economy of nature, whether viewed 

 as to its physical, physiological, or meteorological 

 aspects. One fundamental point on which we have 

 at present very little information of anything like a 

 definite character is as to the number of solid par- 

 ticles present in the atmosphere. We know that 

 they are very numerous, and it seems probable that 

 the number varies under different conditions of 

 weather, but what number of particles are really 

 present under any conditions, and how the number 

 varies, we have at present very little idea. In this 

 field of research the physiologists are far in advance 

 of the physicists, as they have devised means of 

 counting the number of live germs floating in the 

 atmosphere, and already we have a good deal of 

 information as to how the number varies under 

 different conditions.' 



Before describing the living particles in the 

 atmosphere we allude to some recent investigations 



260 



