THE PHOSPHORESCENTS 125 



101. The Luminous Bacteria as Tests for Enzymes. 



The different behaviour of Ph. phosphorescens and Ph. PJlugeri towards 

 maltose can be utilised when it is desired to ascertain whether this sugar is 

 produced in any diastatic process. For this purpose plate cultures of the two 

 organisms are prepared,_a mixture of sea-water with 8 per cent, of gelatin, i per 

 cent, of peptone, and J per cent, of boiled potato-starch being used. On these 

 cultures are placed small drops of a solution of the substance whose saccharifying 

 properties are to be tested. Then, if this elaborates glucose or levulose from the 

 starch, the (thickly sown) plates will shortly become luminous at the points 

 affected, whereas if maltose alone is formed, the culture of Ph. Pfliigeri will 

 remain dark. In point of delicacy this reaction has but one compeer, viz., the 

 Bunsen flame reaction, whilst in respect of the duration of the phenomenon it is 

 unequalled. The method may also be used with advantage in the solution of the 

 question whether any given microbe has the power of elaborating an enzyme, 

 and if so, of what nature. Thus, for instance, if Saccharomyces Kefyr, a higher 

 fungus occurring in Kephir granules, is to be tested on this point, a plate culture 

 thickly sown with Ph. phosphorescens is prepared in a medium composed of 

 sea-water, gelatin, and peptone. On several of these non-luminous plates are 

 laid a couple of drops of an aqueous solution of lactose, on others cane-sugar, and 

 on a third series raffinose, none of which sugars are taken up by the photo- 

 bacterium, and consequently the plat?s remain dark. The drops are quickly 

 absorbed by the gelatin and formed patches named by Beyerinck diffusion-fields, 

 in the vicinity of Avhich inoculating streaks of Saccharomyces Kefyr are then 

 drawn, and, on developing, finally enter the field of diffusion. After a short 

 time the colonies of Ph. phosphorescens gradually begin to become luminous at 

 the points where the diffusion-fields are in contact with the Saccharomyceles 

 cultures, this luminosity occurring in all three series, and thus proving that 

 Saccharomyces Kefi/r produces an enzyme (known as lactase) which penetrates 

 into the diffusion-fields of the lactose, saccharose, and raifinose and inverts these 

 di- and tri-saccharides to assimilable hexoses, which then cause the photo- 

 bacterium to become luminous. 



102. The Phosphorescents. 



The question whether the light proceeds from within the organisms, or 

 whether they are in themselves dark, but excrete luminoas metabolic products 

 into the surrounding medium, has been much disputed. The latter opinion 

 was upheld, notably by BR. RADZISCEWSKI (1.), according to whose exhaustive 

 researches the aldehydes and aldehyde-ammonia derivatives are, in general, 

 endowed with the faculty of becoming luminous in alkaline solution, and are 

 thereby gradually oxidised by atmospheric oxygen. The quantities coming into 

 play per unit of time are comparatively small ; a solution of 1.8 grins, of lophin 

 in 25 c.c. of caustic potash remaining luminous for over three weeks. If, then, 

 the fact be remembered that the photobacteria are luminous only in alkaline 

 nutrient media, and in presence of compounds which are partly already aldehydes 

 (especially the sugars) and partly exhibit a similar constitution (e.g. glycerin and 

 asparagin) ; and if it be also remembered that the luminosity only occurs in 

 presence of oxygen, and that in the cultures acids, i.e. oxidation products, are 

 formed from the said luminous materials, then it will be readily understood 

 why Radziscewski sought the source of this beautiful phenomenon, not in the 

 bacterial cell, but in aldehydic metabolic products, phosphorescents, which are 

 oxidised, with evolution of light, outside the organism. The same opinion is 



