542 RESPIRATION AND FERMENTATION 



Respiration does, indeed, increase slightly in some plants as the pressure 

 of oxygen rises 1 , but the much more marked increase produced by a high 

 temperature does not exercise any injurious effect. Moreover the presence 

 of a superfluity of a nutrient substance often induces an increased con- 

 sumption, and in certain cases small doses of poison may produce more 

 active growth, respiration, and production of heat (Sect. 104). Beyond 

 a certain limit of temperature, and beyond a particular concentration either 

 of poison or of food-material, the plant is injuriously affected and ultimately 

 killed. The action of an increased density of oxygen is of similar character, 

 and, as Bert showed, pure oxygen at atmospheric pressure exercises the 

 same influence as air under a pressure of five atmospheres. The mechanical 

 effect of an increased pressure is but slight, and it is more marked in the 

 case of tissues than with isolated cells or cellular filaments ~. 



An increased pressure of oxygen acts in a similar manner upon 

 obligate anaerobes, for the movement of butyric bacteria ceases more 

 or less rapidly according to the partial-pressure of oxygen to which they 

 are exposed, death ensuing in a few hours or a few days 3 . The meta- 

 bolism of aerobes is not markedly altered by an injuriously high partial- 

 pressure of oxygen, and hence the latter may possibly exercise some 

 poisonous effect or other. In anaerobes the metabolic disturbances induced 

 by the presence of oxygen may suffice to produce the injurious effects 

 observed, and, as is always the case when the conditions are unfavourable to 

 continued vital activity, death must ultimately ensue unless a dormant resting 

 condition can be assumed. 



P. Bert 4 first studied the effects produced by a rise in the pressure of oxygen, 

 Johannsen observed the influence upon respiration, and Jentys that upon growth. 

 In their works the older researches are mentioned and a description given of the 

 apparatus employed. In Sect. 98, and in the works of Wieler and Stich, the 

 methods are given for experimenting in rarefied air. Cultures of anaerobic bacteria 

 in gelatine tubes exposed to air form colonies only in the deeper layers of the 

 gelatine, and the closeness with which they approach the surface affords a direct 

 indication as to their sensitiveness to oxygen. 



1 Johannsen, I.e., p. 714, for further literature. Jentys, I.e., p. 457. In pure oxygen the 

 respiratory quotient remains the same. Godlewski, Jahrb. f. wiss. Bot., 1882, Bd. xin, p. 522; 

 Bonnier et Mangin, Ann. d. sci. nat., 1884, vi. ser., T. xvm, p. 364; 1886, vii. sen, T. n, p. 370. 



2 Cf. Jentys, 1. c., pp. 455, 463; Jaccrird, Rev. gen. d. Bot., 1893, T. v, p. 383. 



3 Liideritz, Zeitschr. f. Hygiene, 1889, Bd. v, p. 157. Cf. also Pasteur, Compt. rend., 1861, 

 T. T,n, p. 340, and Etude s. 1. biere, 1876, p. 293 ; Grossmann u. Mayershausen, Archiv f. Physiol., 

 1877, Bd. xv, p. 245; Beyerinck, Butylferment, 1893, p. 6; Centralbl. f. Bact., 1895, Abth. ii, Bd. I, 

 p. 1 12. 



4 P. Bert, Compt. rend, 1873, T. LXXVII, p. 531; Ann. d. chim. et d. phys., 1876, v. ser., 

 T. vn, p. 146 ; La pression barometrique, 1878, p. 856; \Vieler, Unters. a. d. Bot. Inst. z. Tubingen, 

 1883, Bd. I, p. 189; Slich, Flora, 1891, p. i. 



