INSTANCES AND CAUSES OF LUMINOSITY 385 



no special stimulation being necessary as it is in the case of Noctiluca l . In 

 this organism and in Ceratiwn tripos the luminosity appears as the result 

 of a shock-stimulus. It is possible that sudden changes of temperature or 

 of concentration may temporarily increase or diminish the production of 

 light in Fungi and Bacteria. These changes are usually but slight in 

 amount, the organism rapidly adjusting itself to the new conditions. In 

 some cases spontaneous increases and decreases in the intensity of the 

 illumination are shown, but the causes of these are unknown. 



Certain resistant organisms may continue to produce light at tem- 

 peratures or in concentrations which ultimately cause a cessation of the 

 luminosity or even death. In some cases gradual accommodation is possible, 

 so that the organism or its descendants become luminous at temperatures 

 which at first inhibited the production of light. Since variations in the 

 production of light are readily perceptible, they may be used as indications 

 of the vital activity upon which they are dependent. Beyerinck has in 

 fact used luminous Bacteria as a test for the evolution of oxygen, and by 

 means of his auxanographic method has determined the value of different 

 nutrient materials or of metabolic products for the production of light. 

 Owing to the after-effects already mentioned and to other physiological 

 peculiarities care is, however, needed in interpreting the results. 



The influence of temperature. All observers agree as to the existence of an 

 optimum temperature for luminosity. The optimum lies between 25 and 30 C. in 

 the case of Rhizomorpha 2 , the minimum between i and 3 C. Similarly only approxi- 

 mate values have been obtained for Bacteria, and the divergences between the results 

 of different authors are due partly to incorrect naming, and partly to the influence of 

 dissimilar nutrient and cultural conditions 3 . Various Bacteria are still luminous at 

 o C. to 5 C., whereas McKenney found that Photobacterium indicum (Beyerinck), the 

 Bacillus phosphorescent of B. Fischer, ceases to emit light at i5C., the optimum lying 

 between 22 to 28 C., the maximum between 30 and 35 C. In the case of Photo- 

 lacterium (Microspird) luminosum the cardinal temperatures are ioC., i5C., and 

 22 C. respectively. Here and in other cases also the maximum temperature for the 

 production of light lay 5 to ioC. below that for growth. McKenney found that 

 the minimum temperatures for growth and for luminosity were the same, but the 

 results of other observers show that this is not always the case. 



Various workers have observed that light continues to be given off for a certain 

 time after the luminous organism has been cooled below zero or even to 12 C.* 



1 Biitschli, Protozoan, 1883-7, 2 - Abth., p. 1088; Kruckenberg, Centralbl. f. Physiologic, 1887, 

 Bd. I, p. 689; Massart, Bull, scientifique de la France et de la Belgique, 1893, T. xxv, p. 76. 



2 Ludwig, 1. c., p. 35 ; Brefeld, 1. c., p. 4. Wood has been observed to emit light at o C. by the 

 older observers. Cf. Ludwig, I.e., p. 25. Fabre (I.e., p. 187) finds that Agaricits olearius emits 

 light only above 3 or 4 C. 



3 B.Fischer, I.e., 1887, p. 78; 1888, pp. 89, 139; Lehmann, I.e., 1889, p. 789; Beyerinck, 

 1. c., 1891, pp. 8, 66; Eijkmann, I.e., 1892, p. 656; McKenney, I.e., p. 219. 



* B. Fischer, 1. c. ; Lehmann, 1. c. ; Tarchanoff, 1. c., p. 247. Suchsland (1. c., p. 80) found that 

 after cooling to 80 C. the luminosity of certain resistant Bacteria returned on warming. 



PFEFFER. lit C 



