414 PHYSIOLOGICAL LIGHT. 



as putrefaction appears, the luminosity which they imparted to these 

 cadavers ceases. Some Photobacteriacece live in a state of symbiosis 

 upon species of animals that possess a luminosity of their own (Pholas 

 dactylus, Pelagia noctiluca). In other cases they behave like true path- 

 ogenic parasites. When introduced, either accidentally or experimen- 

 tally, under the carapace of certain marine or terrestrial Crustacea 

 (Tulytres, Cloportes), they develop and invade the entire body. The 

 animal thus invaded becomes luminous, but it shortly dies. The 

 attempts made to inoculate animals of higher organization with these 

 pathogenic microbes have hitherto failed. {Still, it is quite probable 

 that the cases of phosphorescent urine, saliva, sweat, and even 

 wounds, observed principally in man, have had no other cause — an 

 important matter to definitely ascertain. Unhappily for science, exam- 

 ples of these singular affections, which, by the way, do not appear to 

 be dangerous, are more rare than those of mammals that become lumi- 

 nous after death. Besides the phosphorescence of the human cadaver, 

 which has been observed several times, there have occurred in butchers' 

 stalls and slaughterhouses true luminous epidemics affecting sometimes 

 pork, sometimes beef sometimes horse meat. In the general physio- 

 logical laboratory at Lyons, a case of luminosity in the domestic rabbit 

 has been recently studied, and from it was prepared, for the first time, 

 a pure culture of a photobacterium of the flesh of mammals, the Photo- 

 bacterium sarcophilum (fig. 1). This discovery has led to the elucidation 

 of several important points in the biology of these curious parasites. 



The Photobacteriaceoe usually have the form of an elongated sole; 

 their length varies between 2 and 4 pi and their breadth between 1 and 

 2 jj 1 . Some seven or eight species, or perhaps varieties, are distin- 

 guished. Some are very polymorphous and may change into micro- 

 cocci, into commas, into filaments, without ceasing to be luminous. 

 At other times, while the form remains the same, the photogenic func- 

 tion may be made to disappear by slightly modifying the culture 

 medium, and inversely, the bacteria which have been extinguished may 

 by the same means be lighted up again even after quite a long time. 



These facts show that the photogenic function is independent of the 

 form of the creature. These microbes are readily cultivated in bou- 

 illon of gelatin peptone containing 4 per cent of sea salt. While the 

 Photobacterium sarcophilum develops well in liquid bouillons, it is the 

 first photogenic microbe which has been successfully cultivated in 

 a fluid medium containing only substances having a definite chemical 

 composition, such as water, glycerin, phosphates, asparagin, sea salt. 

 It also presents a peculiarity not found in other species, and which it 

 is well to note, because it may explain why certain pathogenic agents 

 infect all individuals without distinction, while others attack only those 

 which have a special, morbid predisposition. With the exception of 



■The /x, which is the unit of length in micrography, is equal to the thousandth of 

 a millimeter. 



