186 TEXT-BOOK OF BACTERIOLOGY. 



this species, often continuing- for months in our artificial cultures, 

 and thus admitting 1 of extended examination, we shall devote some 

 space to the consideration of this micro-organism. 



Take a number of fresh sea-fish which have not yet become dry' 

 on the outside haddock or herring- are the best and keep them 

 beween two plates at about 15 C. As a rule, at the end of twenty- 

 four hours some of them show shining- spots which soon increase 

 in size, and often on the second day spread over the whole body. 

 Later on, as the decomposition begins and progresses, the phos- 

 phorescence diminishes gradually in intensity and at last disap- 

 pears altogether. 



In this same manner other kinds of food (bread, raw beef, fat, 

 etc.) become phosphorescent, and as investigations thus far made 

 have shown, always in consequence of the presence of one and the 

 same micro-organism which has been described by Fischer as Bac- 

 terium phosphorescens. 



It is a short, thick rod-cell with rounded ends which frequently 

 forms globe-like cells, when a rapid fission of the rods takes place, 

 thus reminding us in its outward behavior of Micrococcus prodigio- 

 sus. Like this, its cells often cohere in twos or threes, and occa- 

 sionally form long threads. We must mention, too, the regular 

 and early occurrence of involution forms, which often take a very 

 peculiar shape. It is not motile; the existence of spores has 

 not yet been observed. Like the other phosphorescent bacteria, it 

 can be stained without difficulty with the ordinary anilin colors. 



On the gelatin plate its colonies develop at a moderate rate. 

 They are small, white, and have a gleam like that of mother-of- 

 pearl, never become larger than a pin's head, and never under any 

 circumstances liquefy the food medium. Under the microscope 

 they appear as small, roundish, yellowish- white drops with sharply- 

 defined but irregular edges and granular contents, often arranged 

 in several concentric layers. 



In the test-tube culture the growth proceeds all along the punc- 

 ture in white globular grains, yet far more luxuriant at the sur- 

 face, where a gra3 r ish-white thin coating forms, which occasionally 

 breaks up into separate flakes. In older cultures the culture me- 

 dium becomes of a yellowish-brown color in the vicinity of the bac- 

 terial coating. 



Scratch-cultures, on obliquely-hardened gelatin, show a thick 

 growth, which is confined to the immediate vicinity of the inoculat- 

 ing scratch; also on oblique agar and potatoes the growth does 

 not extend far beyond the inoculated portion. 



The Bacterium phosphorescens does not thrive at the tempera- 



