RELATION OF BACTERIA TO TEMPERATURE. 23 



the periods are much longer. Anthrax spores will survive 

 drying for several years, but here again moisture enables 

 them to resist longer than when they are quite dry. When 

 organisms have been subjected to such hostile influences, 

 even though they survive, it by no means follows that they 

 retain all their vital properties. 



Relation to Gaseous Environment. The relation of 

 bacteria to the oxygen of the air is such an important 

 factor in the life of bacteria that it enables a biological 

 division to be made among them. Some bacteria will only 

 live and grow when oxygen is present. To these the title 

 of obligatory aerobes is given. Other bacteria will only grow 

 when no oxygen is present. These are called obligatory 

 ancerobes. In still other bacteria the presence or absence 

 of oxygen is a matter of indifference. This group might 

 theoretically be divided into those which are preferably 

 aerobes, but could be anaerobes, and those which are pre- 

 ferably anaerobes, but could be aerobes. As a matter of 

 fact such differences are manifested to a slight degree, 

 but all such organisms are usually grouped as facultative 

 ancerobes, />., preferably aerobic but capable of existing 

 without oxygen. Examples of obligatory aerobes are 

 B. proteus vulgaris, B. subtilis ; of obligatory anaerobes, 

 B. tetani, B. cedematis maligni, while the great majority of 

 pathogenic bacteria are facultative anaerobes. With regard 

 to anaerobes, hydrogen and nitrogen are indifferent gases. 

 Many anaerobes, however, do not flourish well in an atmo- 

 sphere of carbon dioxide. Very few experiments have 

 been made to investigate the action on bacteria of gas 

 under pressure. A great pressure of carbon dioxide is said 

 to make the B. anthracis lose its power of sporing, but it 

 seems to have no effect on its vitality nor on that of the 

 B. typhosus. With the bacillus pyocyaneus, however, it is 

 said to destroy life. 



Temperature. For every species of bacterium there is 

 a temperature at which it grows best. This is called the 

 "optimum temperature." There is also in each case a 

 maximum temperature above which growth does not take 



