TEXT-BOOK OF BACTERIOLOGY. 187 



ture of the incubator, and even at 30 C. its development is but 

 slight. It thrives best at 15 or 25 C. Yet according- to the in- 

 vestigations of Forster, Tilanus, and Fischer, it can, like the indi- 

 genous glow bacillus, live and increase even below C. 



It is a semi-anaerobic micro-organism, which, in a space deprived 

 of oxygen, in an atmosphere of hydrogen, or even of carbonic acid, 

 continues to grow. The development of phosphorescence is depend- 

 ent on the access of air i.e., on a process of oxidation, both in Bacil- 

 lus phosphorescens and also in the two other glow bacilli. There- 

 fore this phenomenon is seen only in the upper portion of puncture 

 cultures, and disappears lower down; its occurrence is restricted 

 to the same degrees of temperature which were mentioned as im- 

 portant for the development of the bacillus itself i.e., between 

 and 25 C. While the West Indian and the indigenous baciHi show 

 a bluish light, the glow of Bac. phosphorescens is greenish or 

 greenish-white. It is, under some circumstances, so considerable 

 that by the light of a gelatin plate or of one of Esmarch's rolled 

 tubes the hands of a watch can be recognized on the dial-plate, and 

 Fischer has even succeeded in photographing the shining cultures 

 by their own light. 



It is worthy of mention that cultures of Bacterium phosphores- 

 cens which once show this property retain it sometimes for months. 

 In other cases it disappears much sooner, only lasting a few days 

 during the commencement of the development and gradually dying 

 away. This is specially noticeable when the bacteria have been 

 kept a long time and through many generations on our ordinary 

 gelatin. Here they fall a prey to natural attenuation, and at last 

 lose their luminous power altogether. Yet there exists a means by 

 which it can be restored at any moment, and which has never yet 

 failed ; this is the addition of 2 or 3$ of common salt to the arti- 

 ficial food medium. On gelatin prepared in this manner the growth 

 of the bacteria is particularly luxuriant, and the phosphorescence 

 always appears clearly and strongly even if the very last traces of 

 it had disappeared from previous cultures. Natural or artificial 

 sea-water and the surface of boiled fishes are also an excellent field 

 for the display of the luminous phenomenon. Contrary to the 

 other two glow bacilli, the phosphorescence when transmitted to 

 boiled fishes yields a light that is confined to the point of inocula- 

 tion. 



How the phosphorescence is produced is not yet known with 

 certainty. As we know, Lehmann and Tollhausen attribute it to 

 an intra-cellular process, saying that as from the protoplasm heat, 

 carbonic acid, etc., are developed by molecular metabolism, so also 



