Significance of Functional Metabolism in the Plant. 97 



the final product of physiological combustion, while in the nitro- 

 bacteria the same is the case with nitrous or with nitric acid. There 

 can be no question that as time goes on, yet other specific peculiarities 

 will be discovered. Thus it is conceivable that certain micro- 

 organisms may gain their chemical kinetic energy by the oxidation 

 of ferrous oxide, and others perhaps,* by the oxidation of hydrogen 

 or of the gaseous hydrocarbons. 



Considered from the general point of view of energy, it is by no 

 means necessary that physiological combustion should proceed 

 along the same lines in all organisms. Indeed it was only in con- 

 sequence of an unjustifiable generalisation from observations on the 

 higher animal and vegetable organisms, that the belief arose that 

 organic life is impossible without the agency of free oxygen, i.e., 

 without oxygen-respiration. Just, however, as man is able to 

 employ driving power, derived from such reactions as the explosion 

 of gunpowder or dynamite in a space free from oxygen, so must it 

 appear a priori possible, that organisms have been evolved on our 

 earth, in adaptation to special conditions and necessities of life, which 

 are able to live without making use of free oxygen. 



As a matter of fact numerous anaerobic micro-organisms are now 

 known. Their existence, indeed, was established as long ago as 

 1861, by the investigations of Pasteur, and it was only the deeply 

 rooted belief in the absolute indispensability of oxygen-respiration 

 which caused the majority of the learned to remain sceptical, or to 

 endeavour to save the dogma of the necessity of oxygen by forced, 

 and often, frivolous interpretations. 



Much, it is true, remains to be explained as to the details of meta- 

 bolism, both in aerobic and anaerobic organisms ; meanwhile this 

 at least is certain, that even in anaerobes, kinetic energy is gained 

 by means of a great variety of chemical transformations. This fact 

 is at once indicated by the various final products of functional meta- 

 bolism, in one organism consisting chiefly of alcohol and carbonic 

 acid, in another of butyric acid, lactic acid, or butyl-alcohol, 

 or of other very various volatile and non-volatile compounds, 

 which, however, often owe their origin in part to secondary pro- 

 cesses; considered from the standpoint of energy it is not neces- 

 sary that any gaseous products should arise, or even that oxygen 

 atoms should be transposed, or carbon compounds disintegrated. 

 It is true that the latter assumption holds good in all cases which 

 have as yet been minutely studied, but it is quite conceivable that 

 kinetic energy may be obtained by some other reaction (for example, 

 by the reaction between potassium nitrate and sulphur). 



The anaerobia are, however, of great importance in the economy 

 of nature, for by their agency decomposition is carried on in the 

 interior of the cadaver, and generally in places where the conditions 



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