THE BIOLOGY OF MICROBES, ETC. 143 



emits light with peptone and glucose. It measures 

 from 1'5 to T9 //, in length, and from 1 -3 to 17 //, in 

 breadth ; these rods have rounded ends, and appear 

 to divide exceedingly rapidly. The bacterium is 

 motionless, and occurs singly, and sometimes in 

 short chains. ' On plates prepared with peptone 

 gelatine, to which a small quantity of glucose, and 

 from 2 to 3 per cent, of common salt have been 

 added, the microbe develops luxuriantly, giving 

 rise to small, white, mother-of-pearl-like colonies, 

 about the size of a pin's head, with no surrounding 

 zone of liquefied gelatine.' This microbe is readily 

 obtained by placing fresh cod or herring (with moist 

 surfaces) between a couple of plates, and kept at 

 about 20 C. for twenty-four or thirty-six hours. 

 At the end of this time small phosphorescent points 

 or dots are seen to glow on the surfaces of the fishes. 

 These dots are colonies of the microbe in question. 



Bacterium Fischeri. Unlike the preceding phos- 

 phorescent microbes, B. Fischeri liquefies peptonised 

 gelatine ; and by the addition of a small quantity of 

 sugar the intensity of the phosphorescence is in- 

 creased. The microbe is motile, and occurs singly 

 and in short chains. It grows on agar-agar at a 

 low temperature (from C. to 15 C.). 



Bacterium Balticum. Like the preceding microbe, 

 B. Balticum was found in the waters of the Baltic, 

 and also liquefies peptonised gelatine. 



The four forms of phosphorescent bacteria can- 

 not develop their lighkemitting functions to their 

 highest point without the presence of some substance 

 from which carbon may be easily obtained, such as 



