PHOSPHOEESCBNT BACTERIA 283 



in chloroform. On extracting the growth from a number 

 of agar cultures of the B. joyocyaneus with chloroform, 

 and filtering, a deep- blue solution is obtained, which on 

 slow evaporation in the dark yields a crystalline residue of 

 pyocyanine. 



The cultural characters of a number of chromogenic 

 bacteria will be found in the last chapter. 



Phosphorescent Bacteria. — Many bacteria give rise to 

 phosphorescence as a result of their vital activity. It is 

 to these organisms that the beautiful phosphorescent phe- 

 nomena sometimes seen in the, sea, especially in the 

 tropics, are due. They are also seen not infrequently in 

 marshy places and on decaying wood ; the luminescence 

 occasionally exhibited by fish is also well known. The 

 light given off from the gelatine cultures of some of these 

 bacteria is sufficient to enable one to ascertain the time by a 

 watch in a perfectly dark room, and even photographs have 

 been taken by the light emitted by these organisms. 



Beyerinck, who has carefully studied the light-giving 

 bacteria, finds that the formation of light does not bear any 

 direct relation to the growth of the organisms ; but he finds 

 that certain food substances are necessary for them to pro- 

 duce light. For instance, some require oxygen, although 

 they will grow perfectly well under anaerobic conditions, 

 without producing phosphorescence. 



Other Products of the Metabolism of Micro-organisms. — In 

 putrefactive fermentation, a number of substances are pro- 

 duced by the agency of bacteria. In addition to the very 

 numerous and various bodies produced in the many fer- 

 mentative processes — such as acetic, lactic, butyric, and 

 other acids, alcohols, ammonia, albumoses, ptomaines, 

 colouring matters, etc., of which many have been described 

 in the previous pages — are a large number of other bodies, 

 of which the following are a few which occur in the various 



