THE BACTERIA OF COLOUR AND PHOSPHORESCENCE. 353 



to i.p/i long and 1.3 to 1.7^ broad ; these rods have rounded ends 

 and appear to divide exceedingly rapidly, in consequence of which 

 the cells are usually almost round, and are then very like large micro- 

 cocci, in fact they are sometimes compared to the Bacillus prodigiosus 

 which was for long spoken of as a micrococcus. Sometimes a few organisms 

 may be held together in a short chain ; the bacterium is motionless, and no 

 spores have as yet been observed. On plates prepared with peptone gelatine, 

 to which a small quantity of glucose, and from two to three per cent, of 

 common salt have been added, the organism 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. Under the microscope 

 these are seen as small, round, yellowish-white, granular drops, with sharp 

 but irregular margins. 



Another organism, the Photo-bacterium Fischeri, found in 

 the waters of the Baltic, peptonizes gelatine, causing it to 

 liquefy very rapidly. It can exist in a medium to which a 

 small quantity of raw sugar has been added, this addition of 

 sugar increasing in a most remarkable manner the intensity 

 of the light given off, although a large quantity of the same 

 material (three to five per cent.) interferes with, or altogether 

 stops, the phosphorescent activity of the organism. This 

 organism is motile ; it occurs in short chains and grows on 

 gelatine and agar, the former of which is liquefied by its 

 action. Grown on plates, the colonies after making their 

 appearance emit a kind of bluish-white light, and the 

 organisms themselves as they lie at the bottom of the fluid 

 gelatine have also a somewhat bluish tinge. It grows best 

 at a low temperature, from 15 down to o C., or even lower. 



Photo-bacterium Balticum also liquefies gelatine, but more 

 slowly than the above. It is not, however, dependent upon 

 glycerine for its growth, and is not nearly so sensitive to the 

 presence of a considerable quanity of sugar, as it can live in 

 a medium containing from three to five per cent, of that 

 substance. These four forms are all what may be called pep- 

 tone carbon bacteria, as they cannot develop their functions 

 to their highest point without the presence of some sub- 

 stance from which carbon may be readily obtained such as 

 sugar, glycerine, glucose, &c., as well as peptone, but the 

 Photo-bacterium Fischeri and Photo-bacterium Balticum 

 do not set up any ferment action as do the first two 

 mentioned. 



Beyerinck states that all four are best cultivated in fish 

 broth made with sea-water, to which are added one per cent. 



24 



