144 A MANUAL OF BACTERIOLOGY 



glycerol, glucose, asparagine, sugar, etc., as well as 

 peptone. For this reason they have been termed pep- 

 tone-carbon-bacteria. Beyerinck, 1 who has recently 

 studied these microbes, states that they are best 

 cultivated in fish broth with sea-water, to which are 

 added 1 per cent, of glycerol, 8 per cent, of gelatine, 

 and i per cent, of asparagine. 



Photo- Bacterium Indicum. This microbe occurs 

 in the West Indian Sea. It liquefies gelatine very 

 rapidly ; and the greatest intensity of light is given 

 off when the culture is kept between the tempera- 

 tures of 30 and 35 C. 



Bacterium luminosum. This microbe, which is 

 most active at about 15 C., is found in the North 

 Sea. Both the preceding and the present microbes 

 give off light in peptonised gelatine without requiring 

 the presence of sugar or any other carbohydrate, conse- 

 quently they have been termed peptone-bacteria. 



In all these bacteria (phosphorescent) the develop- 

 ment of luminosity is constantly accompanied by 

 the transition of peptones into organised, living 

 matter, under the influence of free oxygen, with or 

 without the concurrence of another compound con- 

 taining carbon. 



Certain other bacteria, although they do not emit 

 light, are influenced by it, among these are the two 

 following microbes : 



Bacterium chlorinum. The cells are from 2 to 3 

 fi in length, and are motile. This microbe accumu- 

 lates in the light, but only when oxygen is absent. 



1 Transactions of Royal Academy of Sciences of Amsterdam, 

 1890. 



