36 BACTERIA IN DAILY LIFE 



dustrial problems are to be found in the conduct 

 of commercial undertakings of such national 

 magnitude and importance as brewing and agri- 

 culture. But it is not with these beneficent or 

 great industrial classes of bacteria that we are 

 now more immediately concerned, but rather with 

 the malevolent varieties, or the so-called " sub- 

 merged tenth," for which no labour colony has at 

 present been created to direct their energies into 

 useful and profitable channels. 



We know that as regards mere numbers the 

 bacteria in air may vary from o to millions in 

 a couple of gallons, these extremes being de- 

 pendent upon the surrounding conditions or 

 relative purity of the atmosphere. 



Out at sea, beyond the reach of land breezes, 

 it is no uncommon thing to find none whatever ; 

 on mountains and even hills of humble elevation 

 the paucity of bacteria is very marked if there 

 are no abnormal or untoward circumstances con- 

 tributing to their distribution. In illustration of 

 this the recent investigations of the air on the 

 summit of Mont Blanc by M. Jean Binot are of 

 especial interest, inasmuch as the altitude at which 

 they were carried out is the highest at which the 

 search after bacteria has so far been pursued. 

 This intrepid investigator spent no less than five 

 days in the observatory, which is situated on the 



