PHOTOGENIC OR PHOSPHORESCENT BACTERIA 141 



bacterium ' phosphorescens and Photobacterium Pfliigeri towards mal- 

 tose, as a means of ascertaining whether this sugar was or was not 

 produced in any diastatic process. For this purpose a mixture 

 composed of 100 c.c. sea-water, 8 per cent, gelatine, 1 per cent, 

 peptone, and 0'25 per cent, potato-starch is prepared. Then plate- 

 cultures of these organisms are prepared, using this mixture as the 

 nutrient medium. Suppose we wished to test whether a certain 

 solution had diastatic properties, a few drops would be placed on each 

 plate. If these drops contained diastase this would act on the potato- 

 starch and produce maltose. The production of this substance would 

 have no effect on the culture of Ph. Pfltigeri, because this organism is 

 indifferent to maltose, but on the culture of Ph. phosphorescens the 

 presence of maltose will at once be signalised by a perceptible develop- 

 ment of phosphorescence. The method has also been used to ascertain 

 whether any other microorganism has the power of forming enzymes, 

 and also for finding out the nature of these enzymes. For this 

 purpose several gelatine plates of Ph. phosphorescens are prepared. 

 Some of these receive each a couple of drops of the sugar lactose, 

 others the same quantity of cane sugar, and a third lot raffinose. Not 

 one of these sugars can be assimilated by Ph. phosphorescens. The 

 drops are absorbed into the gelatine, and form patches, called by 

 Beijerinck diffusion-fields. Near each diffusion-field the gelatine is 

 inoculated with the organism that is to be tested. This will grow 

 into the diffusion-field. When this experiment is tried with Saccha- 

 romyces Kefyr it results in all three sets of plates becoming phospho- 

 rescent. Now, as phosphorescence appears only after the introduction 

 of Sacchar. Kefyr, it shows that this organism is able to change the 

 three kinds of sugars into other forms which can be absorbed by Ph. 

 phosphorescens and produce phosphorescence ; that is to say, enzymes 

 are secreted by Sacchar. Kefyr, which bring about the change from 

 one sugar to another and more assimilable form. 



Cause of Phosphorescence. There is still a good deal of dispute 

 as to the cause of the luminosity of bacteria. According to one theory, 

 the body of the microbe is dark, the luminosity being produced by 

 a substance excreted by it. This theory is supported by the fact 

 that certain chemical substances, e.g. methyl aldehyde and grape- 



1 Beijerinck uses the generic term "Photobacterium'' to cover all the phos- 

 phorescent bacteria, irrespective of their shape or any other characteristic. The 

 use of the term is not advisable for purposes of classification, and even for 

 descriptive purposes is apt to mislead, owing to the introduction of the word 

 "bacterium." 



