THERMOCENIC AND PHOSPHORESCENT BACTERIA 63 



waste) frequently become heated, the temperature inside the mass being often 

 raised to 60 or 70 C. This spontaneous heating, which may increase to 

 actual ignition (spontaneous combustion), is due to the respiratory activity of 

 aerobic bacteria (thcrmogcnic bacteria of Cohn), which set up fermentation 

 and putrefaction. 



Cohn (33) found in damp cotton-waste a micrococcus which, when well 

 supplied with air, raised the temperature of the decaying mass to 67 C., if 

 care were taken to prevent radiation, carbonic acid and trimethylamine 

 arising as respiratory products. 



Light is another form in which the surplus energy of respiration exhibits 

 itself both in terrestrial and marine plants and animals. The existence of 

 phosphorescent insects is a matter of common knowledge. The mysterious 

 light often seen in old willow-trees is given off by the mycelia of certain 

 parasitic fungi. Among marine organisms there are very many kinds which 

 are luminiferous. The phosphorescence of the sea is mainly due to light- 

 producing infusoria, hydrozoa, and ascidia, and in our latitudes above all to 

 bacteria (34). The various kinds of phosphorescent bacteria have been 

 collected together to form a ' biological ' genus Photobacterium. They include 

 actively motile straight rods and vibrio- like forms, but very few have been 

 completely described, and names like B. phosphorescent, B. luminosus, Vibrio 

 albensis must not be regarded as designating ' good ' species. The faint 

 glow seen upon decaying haddocks, mackerel, and other sea fishes, is pro- 

 duced by these micro-organisms. Whether any phosphorescent bacteria 

 occur in fresh water is doubtful : but all with which we are as yet well 

 acquainted are from the sea. Being marine organisms, the phosphorescent 

 bacteria need in their culture-media from two to three per cent. NaCl, 

 besides the usual salts and peptone, and to obtain successful cultures 

 of phosphorescent bacteria the media must contain these substances, 

 besides some other source of carbon such as sugar, glycerine or asparagine. 

 Phosphorescent bacteria would seem therefore to be ' peptone ' bacteria, 

 saprophytic in the sea upon dead animals and plants, from which they 

 are washed off in countless numbers by the waves. The phosphorescent 

 bacteria of the North Sea and Baltic flourish best at about 18 C., but 

 can grow quite well at much lower temperatures, even down to o C., 

 resembling in this respect the other inhabitants of northern waters. In the 

 absence of oxygen they are indeed able to grow slowly, but are then not 

 phosphorescent, the production of light being an exclusively aerobic pheno- 

 menon. This is evident, too, when we watch the phosphorescence of the 

 sea, for perfectly smooth water does not shine at all, while the brilliancy of 

 the light is always greatest upon the crests of the waves, or where the 

 water is churned up with air in the wake of a ship. That the respiratory 

 exchange (oxidation) of the bacteria is the cause of the phenomenon is 

 proved by the fact that the death of the micro-organisms or exclusion of 



