VITAL PHENOMENA. 193 



Oxygen is also necessary to life. It is \hepabulum 

 vitcs. But the discovery of the beings called by 

 Pasteur anacrobia appears to contradict this state- 

 ment Pfeffer, the illustrious botanist, was certain, 

 in 1897, that the dogma of the necessity of oxygen 

 no longer held good. This is no longer tenable. 

 In 1898 Beijerinck carried out most careful re- 

 searches on anaerobia said to have been cultivated 

 in a vacuum, such as the bacteria of tetanus and the 

 septic vibrion ; or on those to which oxygen seems to 

 be a poison, such as the butyric and the butylic 

 ferments, the anaerobia of putrefaction, the reducing 

 spirilla of the sulphates. All use free oxygen. They 

 consume very little it is true ; they are micro-aerobia. 

 The other organisms, on the contrary, need more. 

 They are macro-aerobia or simply aerobia. Besides, 

 if the so-called anaerobia take little or no free 

 oxygen, it matters little. They take the oxygen 

 in combination. It may be said with L. Errera 

 that they have an affinity for oxygen, for they 

 extract it from its combinations, and that " they 

 are so well adapted to this mode of existence that 

 life in the open air being too easy no longer suits 

 them." There are for the different animal species 

 different optima of oxygen. 



Living beings require a certain amount of heat. 

 Life, which could not have existed on the globe when 

 it was incandescent, will not be able to exist when it 

 is frozen. For each organism and each function 

 there is a maximum and a minimum of temperature 

 compatible with activity. There is also an optimum. 

 For instance, the optimum is 29* C for the germination 

 of corn. 



The condition of the optimum exists in the same 



