THE PHOSPHORESCENTS. 163 



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. pliosphorescens 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 plates remain dark. The drops 

 are quickly absorbed by the gelatin and form patches named by 

 Beyerinck diffusion-fields, in the vicinity of which 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 Saccharo- 

 mycetes cultures, this luminosity occurring in all three series, 

 and thus proving that Saccharomyces Kefyr produces an enzyme 

 (known as lactase) which penetrates into the diffusion-fields of 

 the lactose, saccharose, and raffinose, and inverts these di- and 

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

 bacterium to become luminous. 



102. The Phosphoreseents. 



The question whether the light proceeds from within the 

 organisms, or whether they are in themselves dark, but excrete 

 luminous metabolic products into the surrounding medium, has 

 been much disputed. The latter opinion was upheld, notably by 

 BR. RADZISCEWSKI (L), according to whose exhaustive researches 

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

 endowed with the faculty of becoming luminous in alkaline solu- 

 tion, 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 grms. 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 held in the main by 

 Quatrefages, Owsjannikow, Ludwig, and Dubois, the observer last 

 mentioned designating the assumed phosphorescents luciferin. 

 The most important effect of the photobacteria, viz., marine phos- 



