544 RESPIRATION AND FERMENTATION 



might be due to substances resembling ferments, to molecular vibrations 

 generated by the plasma, or to the continual decomposition and regeneration 

 of certain compounds. Special interactions may occur between the proto- 

 plasm, oxygen, and the compounds consumed in respiration, while at the 

 same time the protoplasm may combine loosely with oxygen and transfer it 

 to the substances oxidized. The absorption of oxygen and the exhalation 

 of carbon dioxide are closely connected processes, for the latter undergoes 

 an immediate and very marked decrease when the former ceases 1 . More- 

 over, the fact that methyl-blue remains intact within the protoplasts even 

 in the absence of all free oxygen, is sufficient to show that the induced 

 affinities for oxygen arc not such as to render the organism capable of 

 obtaining it from any reducible substance *. 



It is therefore impossible to say whether a continual decomposition 

 of proteids is the unavoidable accompaniment of all metabolism involving 

 a liberation of energy, for although many observations point to this 

 conclusion, the mere fact that such decomposition has been shown to occur 

 in certain cases does not warrant such an assumption, and moreover the 

 oxidation of nitrites, sulphuretted hydrogen, &c., may not involve any 

 proteid decomposition whatever. No proteid decomposition can occur 

 if the power of regeneration is absent, and it is not impossible that 

 energy may be obtained by the oxidation of substances which do not 

 enter into direct union with the protoplasm. Moreover it is worthy of 

 notice in this connexion that Saccharontyces and certain bacteria are 

 incapable of anaerobic existence when fed with proteids (Sect. 99). 



Continual proteid-decomposition need not necessarily accompany vital 

 activity, for the energy necessary for the maintenance of the latter may be 

 obtained by the aerobic or anaerobic decomposition of other substances, 

 provided this decomposition actually takes place in the protoplasm or 

 between its component parts, and even when these substances enter into 

 simple association with proteids, as probably occurs during fermentation, 

 no proteid-decomposition is necessarily involved. It is of course essential 

 that the specific constructive elements of the protoplasm, to which it owes 

 its hereditary character, must not be irreparably disorganized however 

 active respiration may be (Sect. 7). 



Metabolic processes liberating energy must take place in all proto- 

 plasmic organs, and it has been observed indeed that isolated fragments of 

 protoplasm continue to respire as long as they remain living. It is, however, 

 also possible that extracellular oxidations which are of service to the plant 

 may be carried out by katalytic action on the surface of the protoplast, 



1 See Pfeffer, Uuters. a. d. Bot. Inst. z. Tubingen, 1885, Bd. I, pp. 672, 677 ; Oxydationsvorgange 

 in lebenden Zellen, 1889, p. 490. 



a Pfeffer, 1889, 1. c., p. 513. Cf. also Sect. ioa. 



