536 RESPIRATION AND FERMENTATION 



varying mixtures of air and hydrogen. The gases evolved may be determined by 

 the usual methods of gas analysis. 



SECTION 99. The Intramolecular Respiration of Aerobes. 



Even in an atmosphere of hydrogen aerobes continue to produce 

 carbon dioxide until death ensues. Anaerobes behave similarly when the 

 food supplied is not such as to permit of anaerobic existence, and it is 

 probable that several metabolic products, and not always the same ones, 

 are produced by the intramolecular respiration of obligate and facultative 

 anaerobes. In all other plants, including both phanerogams and fungi ', 

 the main products appear to be alcohol and carbon dioxide, although, as is 

 shown by the taste or smell, larger or smaller quantities of other substances 

 may be formed, which do not appear when oxygen is present. Hydrogen 

 seems also to be produced by a few of the higher and lower plants, and 

 especially by those which contain mannitc 2 . 



The intensity and character of intramolecular respiration is dependent 

 upon the specific nature of the plant and upon the quality and quantity of 

 the available food- materials. In the absence of fermentable sugar, yeast 

 produces but little carbon dioxide when all free oxygen is removed, and 

 soon dies, even when fed with quinic acid and peptone, a mixture which 

 forms a suitable nutrient medium in the presence of oxygen 3 . The aerobic 

 Mncor stolonifer, Penicillium glaucum, and Aspergillus niger which, ferment 

 sugar slowly, produce much less carbon dioxide in the absence of oxygen 

 than when living aerobically 4 , although more when fed with sugar than 

 with quinic acid, which affords almost equally suitable nutrient material for 

 the aerobic existence of these fungi (Sect. 66). Penicillium and Aspergillus 

 are killed or severely injured by the withdrawal of oxygen for a single hour, 

 but both live a little longer when provided with sugar, than when the latter 

 is replaced by quinic acid. 



1 Muntz (Ann. d. chim. et d. phys., 1876, v. ser., T. vni, p. 86) was unable to detect any 

 alcohol only in the case of Polyporus destructor. 



* Miintz, 1. c., p. 67, and in Boussingault's Agron., Chim. agric. et physiol., 1878, T. vi, p. an 

 (Agaricineae) ; De Luca, Ann. d. sci. nat., 1878, vi. se"r., T. vi, p. 292 (Olives, Ligustrum, &c.). 

 Diakonow (Ber. d. Bot. Ges., 1886, Bd. IV, p. 4) states that Penicillium glaucum, which contains 

 mannite, forms no hydrogen, but this may be due to the feebleness of its intramolecular respiration. 

 Selmi (Bot. Jahresb., 1876, p. 116) has detected an evolution of hydrogen from mould-fungi. The 

 older statements by Humboldt and Marcet as to the evolution of hydrogen by fungi probably arose 

 from experiments conducted in the absence or deficiency of oxygen. 



s Chudiakow, Landw. Jahrb., 1894, Bd. xxm, p. 489; Pfeffer, Unters. a. d. Bot. Inst. 7U 

 Tubingen, 1885, Bd. I, p. 655. 



* Diakonow, Ber. d. Bot. Ges., 1886, p. 2 ; Bot. Centralbl., 1894, Bd. LIX, p. 132. Cf. Pfeffer, 

 1. c., p. 659. 



