AEROBIC AND ANAEROBIC RESPIRATION 547 



same primary causes act in a somewhat different manner 1 . The action 

 may be in part direct, the absence of oxygen influencing the molecular 

 constitution of certain of the substances formed under the changed con- 

 ditions, but there can be no doubt that a stimulating influence is also 

 exercised, modifying the normal chemical or formative activity, or even 

 inducing new processes (Sect. 93). It is therefore possible that the 

 formation of alcohol in the intramolecular respiration of aerobes may 

 arise from a series of processes which are quite foreign to the normal 

 respiratory activity, and indeed various facts point to this conclusion. 

 It is also evident that carbon dioxide cannot be derived from the com- 

 bustion of alcohol in those cases in which the same quantity is produced 

 in the presence as in the absence of oxygen. 



In adaptation to their varying habitats, the anaerobic metabolism of 

 different organisms exhibits widely different characteristics, and a series of 

 modifications which are accompanied by a gradual widening of metabolic 

 activity, lead finally to those aerobes and anaerobes which possess marked 

 fermentative powers. Certain of the new properties thus obtained may attain 

 a more or less inherent character, as for example in those organisms in 

 which intramolecular respiration and fermentative activity are not suppressed 

 by the presence of free oxygen. This is the case in Saccharomyces cere- 

 visiae, &c. (Sect. 103), whereas Mncor racemosus (Sect. 98) and Saccharomyces 

 mycoderma 2 excite alcoholic fermentation in the presence of a little oxygen, 

 but not when the latter is abundant. Similarly the fermentative activity 

 of Bacillus Fitzianus* (ethyl-alcohol from glycerine) is not suppressed when 

 oxygen is supplied, and the same is the case with Bacillus prodigiosus* 

 when sugar is present. An abundance of oxygen, however, inhibits fermen- 

 tation in the case of Gramtlobactcr polymyxa* (butyl-alcohol), and of 

 Bacillus pJiosphoresccns and B. Pfliigeri*, although these require a certain 

 limited supply of oxygen. The formation of hydrogen and sulphuretted 

 hydrogen during putrefaction is largely inhibited by the presence of an 

 abundance of oxygen, either owing to the suppression of intramolecular 

 respiration, or to the direct or indirect oxidation of the products of the latter. 



Free oxygen is always drawn into metabolism to a greater or less 

 extent when present, and hence it must necessarily exercise some influence 

 upon the vital processes 7 , as is the case when yeast consumes more sugar 



1 Cf. Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1885, Ed. I, p. 662 ; Oxydationsvoigiinge, 1889, 

 pp. 497, 510. 



2 Beyerinck, Centralbl. f. Bact., 1895, Abth. ii, Bd. I, p. 74. 



3 Fitz, Ber. d. Chem. Ges., 1876; Buchner, Zeitschr. f. physiol. Chem., 1885, Bd. ix, p. 393. 

 * Liborius, Zeitschr. f. Hygiene, 1886, Bd. I, p. 172. A few other examples also. 



5 Beyerinck, Uber d. Butylalkoholgahrung, 1893, p. 9. 



6 Beyerinck, Aliment photogene, 1891, p. 13 (Sep.-abdr. a. Archiv. Neerlnnd., T. XXIV). 



7 Nageli (.Theorie d. Gahrung, 1879, p. 116) supposes that ferment-organisms are in general 

 less capable of inducing complete oxidation, but this is still doubtful. 



N 11 2. 



