CH. Xl] BACTERIA IN THE SEA 259 



the heart's blood of the animal shewing that it had multiplied in 

 the tissues. 



The distribution of the halibacteria is very wide. H. poly- 

 morphum is the most ubiquitous form and then comes H. roseum 

 and H. pellucidum. They occur at all levels of the sea down to 

 1000 metres. But whereas the bacteria taken from the surface of 

 the sea did not multiply in pure sea water, those obtained from 

 the depths did so. Possibly the strong light at the surface 

 enfeebled them, for at the depths from which the more healthy 

 individuals came there could be little or no sunlight. They 

 occun-ed on the exterior of some fishes and other marine animals 

 taken during the Plankton Expedition. 



Luminous bacteria. Many marine bacteria produce light 

 just as do hosts of other organisms like Ceratium, Noctiluca, 

 worms, deep sea fishes, Crustacea, and other creatures. In the 

 North Sea and Baltic phosphorescence is usually due to Ceratium, 

 and in the Irish Sea to Noctiluca. Often however the light is due 

 to luminous bacteria (Photobacillus or Microspora). Often fish such 

 as herring, mackerel, whiting, &c. are brilliantly phosphorescent, 

 even before decomposition is very evident. I have seen the 

 liquid (water containing alcohol from which most of the latter 

 had evaporated) in a tank containing very imperfectly preserved 

 whiting so very phosphorescent that it emitted quite a strong 

 light. This phenomenon is due to the enormous multiplication 

 of organisms which have been called Photobacteria, the commoner 

 species being P. indicans, P. luminosum, P. pJiosphorescens, &c. In 

 a brilliantly phosphorescent sea the light is only shewn on the 

 surface where the waves break in contact with the air, or are 

 churned up in some way, as by the blade of an oar, or agitated as 

 in the waves thrown off from the bows of a ship, or in the wake 

 of the propeller or paddles. In these cases the luminosity is 

 evoked by the supply of oxygen to the bacteria. But one can 

 often see a net towed beneath the surface of the sea brilliantly 

 phosphorescent. In some cases the phenomenon is certainly due, 

 not to bacteria, but to CeixUiiim or Noctiluca. But whether it is 

 occasioned by bacteria or protozoa the cause is always an oxidation 

 process, and in the case of all organisms displaying it the light is 



17—2 



