112 



luminosum i). In the paper Beijerinck showed clearly that this 

 organism — which under certain conditions is responsible f or the lumi- 

 nescence of the sea water — differs from the ordinaryluminousbacte- 

 ria which practically always can be isolated from sea fish. The state- 

 ments that the pure cultures sometimes splitoff non-luminousforms, 

 and that "dissociation" into two different luminous forms may also 

 occur are noteworthy. Regarding the cause underlying the production 

 of light Beijerinck remarked that this effect is apparently an inci- 

 dental consequence of the respiration process : the energy liberated in 

 this process being converted into visible radiation instead of leading 

 to heat production as usual. 



In a second communication, which appeared simultaneously with 

 the preceding one, Beijerinck dealt extensively with the relations 

 between the luminous bacteria and free oxygen 2). It was shown that 

 suitable suspensions of luminous bacteria have an even stronger 

 affinity for oxygen than reduced indigo carmine has, since, on adding 

 some reducing agent like sodium hydrosulphite to a suspension con- 

 taining the indigo dye the light production continued for some time 

 after the dye had been completely converted into its leuco form. In 

 addition arguments were given in favour of the view that oxygen is 

 also an essential excitation agent for the fermentation and the reduc- 

 tion processes caused by Photobacterium phosphorescens. 



It was not, ho wever, until 1890 that an exhaustive publication of 

 Beijerinck's studies on the luminous bacteria appeared 3). In the 

 first place the various species were divided into two groups, depending 

 on the different nutritional requirements for growth and luminescence. 

 Ph. phosphorescens and related species require for their optimal devel- 

 opment the presence of a nitrogen-free carbon source, such as sugars 

 and glycerol, besides peptone. On the other hand Ph. luminosum and 

 Ph. indicum are to some extent inhibited in their development by the 

 addition of such compounds to the peptone media. The discrimination 

 resulted from the application of the elegant auxanographic method 

 described earlier 4) which can be outlined as follows. A rather large 

 quantity of the cells to be investigated is suspended in an incomplete 

 nutritive medium containing gelatine and by cooling the suspension is 

 solidified in a Petri dish. Then at different spots of the gelatine plate 

 one deposits various chemical substances. If any of these substances 

 supplies the deficiënt nutritive clements growth will occur in the 

 diffusion field of that substance, and will manifest itself by a local 

 increase in opacity of the plate, The consistent application of this 

 method to various luminous bacteria led Beijerinck to a second im- 



1) Arch. néerl. d. sciences exactes et naturelles 23, 401, 1889. 



2) Arch. néerl. d. sciences exactes et naturelles 23, 416, 1889. 



3) Versl. en Meded. Kon. Akad. v. Wetensch., Afd. Natuurk., Amsterdam 3de 

 Reeks, 7, 239, 1890. 



*) Versl. en Meded. Kon. Akad. v. Wetensch., Afd. Natuurk., Amsterdam 3de 

 Reeks, 6, 123, 1889. 



