CHAPTER IV. 



THE. MICRO-ORGANISMS OF OUT-OF-DOORS DUST. 



WE must be on our guard in looking at 

 the results of such analyses as those 

 now to be described against hasty inferences 

 as to their significance. It would be a grave 

 mistake to suppose that living germs in the 

 air are necessarily harmful to human beings, 

 and to infer that air found to habitually con- 

 tain few bacteria is necessarily more salubrious 

 than that which contains more. For the pres- 

 ent, then, let us look upon the results of these 

 analyses simply from the biological standpoint, 

 and, if possible, place ourselves in the attitude 

 of botanists studying the flora of the atmos- 

 phere, not of physiologists concerned with the 

 relationship of these tiny plants to man. This 

 we shall come to by and by when we have ac- 

 cumulated enough facts to justify such infer- 

 ences as may urge themselves upon us. 



