THE VITAL PHENOMENA OF BACTERIA. 131 



Other foci of decomposition probably have their 

 own bacteriological peculiarities which make 

 them' the home of special germs. The germs 

 causing malignant oedema and lockjaw are 

 often found in the earth of gardens. I once 

 happened to find the extremely rare bacterium 

 of the " blood portent " (B. prodigiosus] in a 

 well in Wiesbaden. Other rare species occa- 

 sionally appear upon our nutrient media with- 

 out our being able to ascertain their origin, 

 and then fail to put in an appearance again for 

 years. 



In general the germs provoking fermenta- 

 tion and disease must be reckoned among the 

 rarer species. This is true at least in so far 

 as that such germs generally maintain their 

 power only if they have frequent opportunity 

 to evoke fermentations or diseases. Such 

 opportunity implies the existence of course, 

 of some sort of industry however primitive, 

 which is dependent on fermentation, or of a cer- 

 tain aggregation of men and animals on which 

 to live. 



Even a very rapid flow of air is unable to 

 detach a single bacterium from a moist sur- 

 face, but when the soil or the margin of pools 

 becomes dried up, germs may pass into the air 

 along with the dust ; the only other way in 

 which bacteria can enter the air is through the 



