386 THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



McKenney, however, observed that the luminosity rapidly disappeared below the 

 minimum temperature and above the maximum, while the continued cultivation of 

 Photobacterium indicum at the highest possible temperature raised the maximum for 

 the production of light from 30 to 35C. According to the same author sudden 

 changes produce a shock-effect on the luminosity, whereas other authors have observed 

 slight transitory disturbances of the luminosity to result, especially in bacteria. 

 According to Ludwig 1 , Rhizomorpha becomes temporarily non-luminous when 

 suddenly cooled from 40 to ioC. 



Chemical effects. .Insufficient nutriment naturally produces a cessation of the 

 luminosity more or less rapidly, but the presence of ether or alcohol, as well as 

 changes of composition or concentration of the medium, may allow the Bacteria to 

 grow but not become luminous 2 . Thus in all forms examined hitherto, not only 

 must organic food be supplied, but also inorganic salts. Thus McKenney 3 found 

 that when sodium chloride, sodium nitrate or other salts of sodium, or magnesium 

 chloride formed the only salt present, growth and luminosity were both shown, but 

 that both were suppressed when only a single salt of potassium, rubidium, lithium, 

 ammonium, or calcium was present. The addition of magnesium chloride to the 

 sodium chloride seems to favour luminosity, and hence the ready growth of these 

 organisms in sea-water. The amount of salt may vary between i and 4 per cent, 

 without growth and the evolution of light being perceptibly affected. 



All luminous Bacteria appear to require peptone, while Photobacterium phospho- 

 rescens and P. Pflilgeri seem also to need a suitable carbohydrate, although for 

 Photobacterium luminosum and P. indicum peptone alone suffices. The presence of 

 a large amount of glucose diminishes the luminosity, and Photobacterium luminosum 

 is so sensitive that it ceases to be luminous in the presence of i per cent., and to 

 grow in the presence of 3 to 5 per cent, of glucose. 



Beyerinck worked largely by the auxanographic method, and the slight divergences 

 between his results and those of McKenney are probably the result of dissimilar 

 cultural conditions. In all cases a slight acidity or a somewhat stronger alkalinity is 

 sufficient to inhibit luminosity, and subsequently growth also. Hence at the electrodes 

 in an electrolysed medium containing luminous Bacteria no luminosity is shown if the 

 acid and alkali are set free at the anode and kathode in sufficient amount 4 . Since 

 McKenney found that the luminosity is only shown after movement has ceased, and 

 since it is possible by maintaining the original composition of the medium to keep 

 the organisms permanently motile, it would presumably be possible to grow them as 

 non-luminous forms 5 . 



The production of light is dependent upon aerobic respiration and ceases 

 in the absence of oxygen. This applies not only to aerobic fungi 6 and 



1 Ludwig, 1. c., p. 25. 



a McKenney, 1. c., p. 223; Tarchanoff, I.e., p. 247. Cf. also the works quoted of B. Fischer, 

 Beyerinck, Lehmann, and Katz. 



3 McKenney, 1. c., p. 226. 4 Suchsland, 1. c., 1898, p. 715. 5 Cf. McKenney, 1. c., p. 229. 



6 Fabre, Ann. sci. nat., 1855, 4* sen, T. iv, p. 190; Nees von Esenbeck, Noggerath u. Bischoff, 

 Nova Acta d. Leopold. Acad., 1823, Bd. xi, Th. ii, pp. 667, 694. Boyle showed that oxygen was 

 necessary for the luminescence of wood. Cf. Dessaignes, Journ. de physique et de chimie, 1809, 

 T. LIX, p. 29, and Heinrich, Die Phosphorescenz d. Korper, 1811, p. 334. 



