COLLECTION OF ATMOSPHERIC BACTERIA. 199 



a culture-oven, maintained at a suitable tempera- 

 ture, little colonies of various organisms will form 

 from the germination of spores deposited from the 

 atmosphere. These will soon be recognized by the 

 naked eye, and different species may often be dis- 

 tinguished by peculiarities as to growth, color, etc. 

 It must be remembered that the microbes found 

 in the atmosphere, so far as we now know, are 

 accidentally present, and have originated else- 

 where ; i. e., in decomposing material of organic 

 origin from the surface of the earth. But, while 

 we have no evidence that any known species finds 

 the pabulum necessary for its development in the 

 atmosphere, yet there is nothing improbable in 

 the supposition that this may be true, and that 

 there are species of bacteria which find in the at- 

 mosphere all of the conditions necessary for their 

 rapid multiplication. We know that plants much 

 higher in the scale, which are merely attached to 

 others for support, epiphytes, derive their sus- 

 tenance directly from the atmosphere ; and it is 

 easy to believe that, under exceptional circum- 

 stances as to the presence of organic matter and 

 moisture, especially in tropical climates, or during 

 the summer months in more northern latitudes, 

 some of these minute microscopic plants may also 

 multiply abundantly while suspended in the atmos- 

 phere. 



To judge of the relative abundance of special 

 forms of bacteria in the atmosphere, it will be 

 necessary to resort to direct microscopic examina- 



