388 THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



this organism. Even in this case the production, interaction, and oxidation 

 of these substances are processes of which the former is more especially 

 under physiological control, and so long as the substances in question are 

 kept separate no light would be produced. According to whether the 

 contact took place inside or outside the cell, we should have an intracellular 

 or extracellular production of light l . It is uncertain to what degree the 

 latter occurs, and it must be remembered that the emission of light by 

 excreted slime or mucilage may be due to the presence of luminous Bacteria. 



Whatever the physiological action may be, we have in each case a pro- 

 duction of light by a transformation of chemical energy not involving any 

 appreciable production of heat 2 . Hence light is produced here much more 

 economically than when a body is heated to incandescence by physical or 

 chemical action s . The actual expenditure of energy by the organism in 

 producing the luminous substance is uncertain, but it is of interest to note 

 that energy may be radiated from a cold body to a warmer one which 

 absorbs the emitted light 4 . 



The composition 6 of the light is often that of white light, but in many 

 cases the light has a bluish or greenish tinge. The composition appears, 

 however, to vary according to the cultural conditions, as is shown by 

 spectroscopic examination. No rays resembling the Rontgen or Becquerel 

 rays appear to be present <6 . 



PART III 



THE PRODUCTION OF ELECTRICAL TENSIONS IN THE PLANT 

 SECTION 85. The Origin and Detection of Electro-motive Changes. 



No plants are able like electrical fishes to give perceptible electrical 

 shocks, but nevertheless slight differences of potential capable of maintaining 



1 Noctiluca phosphoresces internally, especially at certain points, and this continues for a little 

 time after the organism has been crushed. Biitschli, Protozoen, 1883-7, Abth. ii, p. 1092. Whether 

 the luminescence of wood is produced in the fungal hyphae or outside of them is uncertain. Cf. 

 Ludwig, Lehrb. d. niederen Cryptogamen, 1892, p. 530. Lehmann (1. c., 1889, p. 789) and Beyerinck 

 (I.e., 1891, p. 52) are wrong in supposing that the cessation of the light on death disproves the 

 existence of a special luminous substance. Beyerinck's supposition that the production of light is 

 connected with the assimilation of peptone has no sure foundation. 



2 [The light might still have a purely physical origin in certain cases without involving any 

 production of special luminous substances. When present these might undergo radiatory atomic 

 disintegration, or might shorten the wave-length of the heat vibrations due to respiration sufficiently 

 to produce visible light rays.] 



8 Langley u. Very, Beibl. z. d. Ann. d. Physik u. Chemie, 1890, Bd. xiv, p. 1096; Dubois, 

 I.e., 1898, p. 376. 



* Wiedemann, Ann. d. Physik u. Chem., 1889, N. F., Bd. xxxvin, p. 485. 



5 Ludwig, Zeitschr. f. wiss. Mikroskopie, 1884, Bd. i, p. 181 ; 1. c., 1892, pp. 78, 537 ; Lehmann, 

 Centralbl. f. Bact., 1889, Bd. v, p. 787 ; Dubois, 1. c., 1898, p. 510. 



6 Suchsland, I.e., 1898, p. 715; Barnard and Macfadyen, Annals of Botany, 1902, Vol. xvi r 

 p. 587; Molisch, Sitzungsb. d. Wiener Akad., 1903, Bd. cxn, Abth. i, pp. 305, 310. 



