Significance of Functional Metabolism in the Plant. 99 



an organism, for example, is yeast (Saccharomyces cerevisice), which, 

 under the nutritive conditions hitherto tested, cannot live without an 

 occasional supply of oxygen, whereas certain bacteria are capable of 

 an unlimited anaerobic life. 



It follows directly from what has been said, that among aerobes 

 life is maintained for a limited time by the action of intramole- 

 cular respiration. For it is only when intramolecular respiration 

 fails that the plant suffers in an atmosphere free from oxygen ; 

 the strictly aerobic mould-fungi keep alive much longer without 

 oxygen, when their aerobic respiratory activity is intensified by pro- 

 viding them with sugar. Thus there is every gradation and transi- 

 tion between those organisms which require free oxygen, and those 

 in which the anaerobic metabolic activity, which is exercised to a 

 certain degree in all organisms, is so far developed and utilised that 

 the functional metabolism suffices for a life without oxygen. Even 

 in aerobes a number of partial functions are carried on for a certain 

 time after the withdrawal of oxygen. Among these functions intra- 

 molecular respiration itself is included, as well as all the metabolic 

 changes with which it is linked. There are also certain processes of 

 growth and movement which are not at once brought to a standstill 

 when oxygen is withdrawn. Thus we know that nuclear division, 

 when it has once begun, still goes on in the absence of oxygen, and 

 under the same conditions the tentacles of the insectivorous Sundew 

 still carry out their movements when stimulated. The muscle of 

 animals can also be caused to contract when deprived of oxygen. 



The relations of the organism to its conditions of life can be 

 demonstrated and understood, even though we do not possess any 

 deeper insight into the causes and the exact processes of functional 

 metabolism. We may also regard it as certain that functional 

 metabolism is indispensable to vital activity, on which in its turn it 

 depends and by which it is regulated, so that metabolism is afc once 

 extinguished when death ensues. Thus the realisation of functional 

 metabolism ensures the continuity of metabolism in general, just as 

 a blazing fire, by heating the wood, constantly creates and maintains 

 the conditions necessary for the continuance of combustion. 



It is also certain that functional metabolism runs its course within 

 the living protoplasm, not merely on its surface or in particular portions 

 of it, but in and between all its constituent parts, as must necessarily 

 be the case in order that vital activity may be maintained. This can 

 be seen at once from the fact that those movements in the protoplasm, 

 or in any separate fragment of the protoplast, which are dependent 

 on aerobic respiration, come to an end on the withdrawal of oxygen, 

 even when the adjoining cells have access to oxygen and are in a 

 state of full activity. 



From the dependence of functional metabolism on vital activity it 



