PHOTOGENIC OR PHOSPHORESCENT BACTERIA 139 



are very rare, of persons suffering from tuberculosis, becoming phos- 

 phorescent. 



The known species belong to quite different families of bacteria. 

 One belongs to the Coccaceae, fourteen to the Bacteriaceae, and four- 

 teen to the Spirillaceae, and of those belonging to the Bacteriaceae 

 some belong to the genus Bacterium, others to the genus Bacillus, and 

 the rest to Pseudomonas. 



The commonest and most widely distributed species is Bacterium 

 phosphoreum. As in a large proportion of cases of phosphorescence 

 this organism is responsible for its production, we must single it out 

 for a detailed description. The individuals are rod-shaped with 

 rounded ends, some being so short that they are almost i-ound. 

 The latter kind are about 1-2 /x in length, whilst the longer ones 

 range from 2 /j, to 7/x. Phosphorescence occurs only if free oxygen 

 be present. The optimum temperature of growth is somewhat low, 

 being about 16°-18°C. This microbe does not grow above 28° C, 

 hence the necessity of cultivating it in a cold room. Like other 

 bacteria it can stand very low temperatures without injury. The 

 light which it emits is of a bluish-green colour, and can be intensi- 

 fied by the addition of small quantities of common salt, potassium 

 nitrate, or potassium chloride. On gelatine plates whitish-yellow 

 phosphorescent colonies with slightly wavy edges are formed. A 

 gelatine stab shows the same type of growth on the surface, and as is 

 to be expected from an aerobic organism, very little development 

 down the stab. Cultivations can easily be made in nutrient agar, on 

 potato, and in milk, in all of which a yellowish-white phosphorescent 

 growth results. Endospore formation is unknown. 



Phosphorescence can be easily obtained by half covering a chunk 

 of beef with a 3 per cent, solution of common salt, and leaving it in a 

 cold, damp room. After one to three days the meat will probably be 

 seen to glow with a bright phosphorescent light. This light is seldom 

 found extending over the whole surface of the meat, but rather 

 emanates from a number of distinct spots. There will be as many of 

 these spots as phosphorescent bacteria that have fallen on to the meat, 

 for each spot of light represents a colony of these bacteria, and each 

 colony has been derived by the growth and multiplication of one 

 individual phosphorescent microbe. 



It is very probable, if this experiment be made, that the organism 

 causing the phosphorescence will be found to be Bacterium phos- 

 phoreum, for this species is most abundant in market places, in 

 slaughter-houses, and in kitchens and cellars. A cultivation of this 



