AEROBIC AND ANAEROBIC RESPIRATION 551 



enzyme may be obtained from Sacckaromyces,vr}\\db is capable of decomposing 

 sugar into alcohol and carbon dioxide l . However this may be, it is quite 

 possible that the energy liberated by an enzymatic decomposition occur- 

 ring in the plasma may be of direct service to the organism. The lactic 

 fermentation of sugar involves only a very slight liberation of energy, 

 and in each case it must be determined whether the fermentative activity 

 is for the purpose of providing a supply of energy, or fulfils quite different 

 functions, whose performance is accompanied by a more or less marked 

 liberation of energy as an accidental corollary. In the caSe of SaccJiaro- 

 myccs alcoholic fermentation may possibly become unnecessary in the 

 presence of oxygen, provided the whole of the energy required can be 

 obtained by aerobic respiration. Many katalytic actions are indeed known, 

 including such simple hydrolytic decompositions as those induced by 

 diastase, &c. (cf. Sect. 91), and formic acid may be decomposed into 

 carbon dioxide and hydrogen by finely divided Iridium, just as in the 

 bacterial fermentation of this acid 2 . 



Various marked decompositions may be induced outside of the proto- 

 plast by means of enzymes, or even perhaps by the transference of molecular 

 vibrations, &c. ; indeed Nageli has suggested that both oxidatory and 

 disintegratory fermentations are extracellular processes. In many cases, 

 however, there is no doubt that the fermentative products are the direct 

 result of metabolic activity ; fungi may produce relatively enormous quanti- 

 ties of partially oxidized organic acids, and thus act as ferment-organisms 

 (Sects. 86 and 95). Moreover, in the intramolecular respiration of aerobes 

 alcohol and carbon dioxide are certainly formed directly by the protoplast, 

 and hence it is possible that the alcoholic fermentation in Saccharomyces is 

 also intracellular. If such fermentative activity is directly connected with 

 metabolism, a knowledge of the causes which regulate the former can only 

 be obtained when a thorough comprehension of the latter has been gained. 

 It is, however, sufficiently clear that the fermentative decomposition of 

 sugar, for example, is not the direct result of the withdrawal of oxygen, 

 and still less can this be the case in those fermentative activities which 

 persist when air is admitted. 



Our knowledge of the inherent protoplastic mechanism is too incomplete to 

 afford a sound basis for any theory concerning the phenomena of respiration, and 

 hence also of fermentation. It is possible that the combination of oxygen with the 

 substances consumed in respiration may be induced by specific molecular vibrations 

 transferred to these substances by the living protoplasm, and Nageli 3 built up 



1 E. Buchner states that the expressed snp of yeast has this power (Her. d. Chem. Ges., 1897, 

 pp. 117, mo\ and his results have been confirmed from several sources. Cf. Sect. 91. 



2 Hoppe-Seyler, Zeitschr. f. physiol. Chem., 1887, Bd. XI, p. 566. Cf. Meyer u. Jacobson, 

 Lehrb. d. org. Chem., 1893, Bd. I, p. 319 



3 Theorie d. Gahrung, 1879, P- 2 9 



