FEEMENTATION 303 



gradually becomes exhausted, and life ceases if the cessa- 

 tion of the supply is prolonged. In the higher plants 

 anaerobic is at the best only capable of supplementing 

 aerobic respiration, and that for but a limited period. The 

 commencing asphyxiation serves as a stimulus to the 

 protoplasm, which responds by setting up the anaerobic 

 changes, but, like all stimulations, the ultimate effect is 

 exhaustion and a failure to continue the response. 



There are other plants, however, which do not require 

 oxygen for their vital processes, and accordingly do not 

 absorb it ; indeed many of them are incapable of carrying 

 on their life in the presence of oxygen. They are of a very 

 humble type, and occur only among the Bacteria and 

 Fungi. An instance may be found in the organisms which 

 induce the formation of butyric acid from sugar or lactic 

 acid. If a few of these are sown in a suitable liquid, and 

 this is then enclosed in a hermetically sealed flask from 

 which free oxygen has been removed, they multiply with 

 extreme rapidity, until indeed either their food supply is 

 exhausted, or the waste products of their metabolism 

 accumulate to an inhibitory extent. If a little free oxygen 

 is admitted their activity ceases and death ensues, or they 

 pass into a resting condition, which lasts as long as oxygen 

 is present. We must not, however, necessarily conclude 

 that their metabolism is of a totally different kind from 

 that of others, but rather that they set up the decomposi- 

 tion and reconstruction of their protoplasm in a different 

 way from those plants which need a supply of oxygen to 

 determine them. 



