64 RESPIRATION OF BACTERIA 



oxygen quenches the light at once, whilst a more abundant supply of 

 highly combustible food-stuffs like carbohydrates increases it. We know 

 of no specific substance (luciferin] to which the luminosity could be due, 

 and the phenomenon is of quite different nature from that exhibited by phos- 

 phorescent bodies like calcium sulphide, for in the bacteria the production 

 of light is quite independent of previous insolation. 



Phosphorescent bacteria may easily be obtained by placing the flesh of 

 fresh haddocks or herrings in a solution of two to three per cent, of NaCl 

 and keeping at a low temperature (5-io C.). In one or two days not 

 merely the fish, but the whole of the liquid in which they lie, give off 

 a pale-greenish light which becomes much more brilliant if a little sugar or 

 glycerine (i. e. respirable material) be added. The bacteria may be readily 

 isolated by the usual methods upon peptone-sugar-gelatine prepared with 

 an infusion of fish and common salt. The pure cultures thus obtained are 

 so strongly phosphorescent that by protracted exposure they may be 

 photographed in their own light. The rays given off are only the more 

 refrangible, from D to G. This is evident, too, from the bluish colour of 

 the light. 



A few words may be said here regarding other marine bacteria (35). 

 The investigations of the German Plankton Expedition show that the 

 prevailing forms are actively motile rods and vibrios, cocci being less 

 numerous. Their distribution is determined mainly by the proximity of 

 land, for the algal vegetation which is richest near the shore attracts 

 myriads of marine organisms that provide the bacteria with a rich variety 

 of nutriment. The influence of the shore extends four or five miles out to 

 sea. The degree of illumination seems without influence, and no regularity 

 could be observed in the distribution, but the number of bacteria per c.c. 

 varies immensely, however far from land the sample be taken, as the 

 following figures show : 



Plymouth Docks (ebb) 13,320 per c.c. 



I mile from shore (flood) 3>96o 



240 miles from shore (Gulf Stream) . . . 645 



450 miles from shore (Sargasso Sea) . 20, 200, 206, 168 



These numbers include the spores of mould-fungi. In 54 per cent, of all 

 samples about 100 germs per ex:, were found ; at depths of from 800 to 

 1,100 metres below the surface only from eight to twelve bacteria were 

 present. 



Specimens of ooze from the ocean bed at depths varying from 1,523 to 

 2,406 metres were sterile ; others again from 4,099 to 5,250 metres contained 

 from one to four bacteria per c.c. This paucity is the more remarkable 

 when we consider that the temperature was from 2 to 5 C., and the 

 conditions altogether such that foraminifera and radiolaria occurred abun- 

 dantly. Possibly the culture-medium (peptonized fish-broth gelatine) was 



