CHAPTER II. 



EFFECTS OF CLIMATE. 



How do these atmospheric microbes first come into 

 existence ? Some investigators still maintain that their 

 carefully conducted experiments show the truth of the 

 theory of spontaneous generation. 



From a strictly scientific, or especially from a biolo- 

 gical, point of view this question is of vast importance, 

 but in the present consideration it is of less moment. 

 We are dealing, not with the origin of life, but with the 

 presence and destruction of microbes, and can afford to 

 regard the more abstruse problem as one of incidental 

 interest only. This, however, we certainly know — that 

 atmospheric microbes may, and do, come from the earth 

 and vegetation, or from the lungs and exhalations of ani- 

 mals. We have no reason for saying that they may not 

 multiply in the air itself, but we know that they are 

 ever floating about us in inconceivable numbers, and 

 that while they are more numerous in cities and towns 

 than in the open country, and in wet places than in a 

 dry soil, yet they are found appreciably everywhere, 

 except, so far as we can ascertain, on the tops of high 

 mountains. Moisture is favorable to their propagation 

 and existence. Some are adapted to live in cold regions, 

 but more require a warm temperature. Changes of 

 weather seem also to favor them, and a marked rise or 

 fall in the barometer has been noticed to affect their 

 numbers and vitality. 



I have observed that in plants which I had kept too 

 warm, and then suddenly exposed to cold, a fungoid 

 growth could be detected in twenty -four hours./ The 

 leaves would then change in color and either shrivel up 

 or wilt. The roots would fail to take - up moisture, the 



