CHAPTER XV. 



PHOTOGENIC BACTERIA. 



99. The Genus Photobaeterium. 



THE first occasion of witnessing the phenomenon known as marine 

 phosphorescence will never be forgotten by the beholder. The 

 boat cleaving the gleaming waves inscribes its track in glittering 

 lines, and every movement of the water causes pronounced phos- 

 phorescence. A rain of sparkling drops of light trickles from the 

 poised oar, each apparently becoming the centre of fresh evolutions 

 of light. This phenomenon, the sight of which is calculated to 

 captivate the senses of the coast-dweller, and lead him to forget 

 all trouble for a time, has a counterpart which filled the mind of 

 earlier races of mankind with terror and lent great support to 

 credulity, viz., the phosphorescence of meat, fungi, and decaying 

 wood in forests. It is only in our own day that an insight into 

 the cause of this wonder has been gained, the microscope, in this 

 case also, being the instrument used to open the door to knowledge. 

 To devote a few words to this phenomenon would be in any event 

 justifiable, on account of its general scientific interest ; and more- 

 over, the matter cannot be avoided in the present work, since 

 some of the facts established in this connection also deserve a brief 

 consideration, both from a chemical and a technical standpoint. 



The first attempt made to investigate this long-known pheno- 

 menon in a scientific manner was that of G. FABRIZIO (I.) in 1592. 

 The treatises subsequently published thereon (up to 1887) are to 

 be found included in a historical and critical review of the subject 

 written by F. LUDWIG (I.). This has been supplemented (up to 

 1891) by a work issued by 0. KATZ (I.) which may be referred to 

 in this place. 



We are indebted to Pfliiger for the first microscopical examina- 

 tion of this phenomenon. He examined, in 1875, the white 

 mucus covering the surface of fish exhibiting a silvery phosphor- 

 escence, and found it composed of globules, frequently united to 

 form chains. When these forms were mixed with water and the 

 mixture passed through a doubled layer of dense filter-paper, the 

 latter became phosphorescent, whilst the filtrate ceased to exhibit 

 this property, thus proving the phosphorescence to be due to the 

 minute organisms themselves. These, which were recognised as 

 bacteria, were in 1878 named Micrococcus phosphoreus by Cohn. 



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