354 BACTERIA. 



of glycerine, one-quarter per cent, of asparagin, and eight 

 per cent, of gelatine. 



The Photo -bacteriun Indicum of the West Indies and 

 the Photo-bacterium luminosum of the North Sea, both 

 liquefy gelatine very rapidly, and appear biologically to be 

 much more like ordinary putrefactive micro-organisms, 

 though the most favourable conditions as regards tempera- 

 ture for the performance of their functions differ somewhat ; 

 that from the West Indies giving off most light at from 30 

 to 35 C., that from the North Sea being most active in 

 this respect at about 15 C. Both of them may multiply 

 and give off light in peptone gelatine without requiring 

 the presence of any sugar ; in fact, they are both extremely 

 sensitive to the presence of this substance, one per cent, 

 preventing the phosphorescence, and three to five per 

 cent, interfering with the liquefaction of the gelatine and 

 eventually killing the bacteria, though, if a small amount of 

 asparagin also be added to the medium in which the West 

 Indian phosphorescent bacillus is growing, light may continue 

 to be given off for some time. The Photo-bacterium Indicum 

 is a motile rod of medium size which grows very readily on all 

 the ordinary nutrient media ; the light is best seen in this 

 case by taking a fish that has been boiled and inoculating 

 with a fragment of the artificial culture ; there then appears 

 in a very short time a soft glistening point, which is 

 found to be covered with bacteria. On darkening the 

 room a beautiful bluish-white light can be seen at the point 

 of inoculation. The light of Photo-bacterium phosphorescens 

 is yellowish. 



Beyerinck gives a number of experiments to show that the 

 formation of light bears no direct relation either to the 

 respiration or to the growth of the organisms, but he finds 

 that certain food substances are necessary for this light to 

 make its appearance, although the growth of the colonies 

 may go on perfectly well without oxygen, even if the forma- 

 tion of light be completely stopped. As soon as the 

 organism is grown anaerobically, certain food substances 

 also become necessary. 



