118 BACTERIOLOGY. 



shaped bacteria. In order to give expression to their 

 characteristic physiological property, they have been 

 grouped together under the generic term photobacterium. 



The property of phosphorescing is even more unstable 

 than that of pigment-production. Nearly all of the organ- 

 isms readily lose their phosphorescence when grown for 

 some time upon artificial media. This is chiefly due to the 

 reaction and composition of the ordinary media. As indi- 

 cated above, the natural habitat of these organisms is the 

 sea, and they require, consequently, a large amount of 

 salt. About 4 per cent, of common salt should be added to 

 the medium, which is still further improved by the addition 

 of small amounts of glycerin and asparagin. The formula 

 for such a medium will be found under B. phosphorescens. 

 On this medium, the phosphorescence develops to a remark- 

 able degree. Some species which have been grown in the 

 laboratory for some years and apparently have lost all 

 power of phosphorescing, promptly develop this property 

 when grown on such media. 



It is quite possible that bacteria will be found inland 

 which ordinarily do not phosphoresce but may do so when 

 developed on media which are rich in salt. The author has 

 observed in Ann Arbor a splendid phosphorescence ou 

 kidneys. The composition of these organs might favor 

 the development of such otherwise non-phosphorescir-g 

 bacteria. Again, the glow observed at times on manure 

 heaps may possibly be due to similar forms favored by the 

 large amount of saline constituents. 



Absence of oxygen and an acid reaction are unfavora- 

 ble to the production of light. The temperature of the 

 body is likewise unfavorable. The very best phosphor- 

 escence is, as a rule, obtained when the growth takes place 

 at about 15. Gelatin tubes and plates under these condi- 

 tions will phosphoresce for more than a month. The phe- 

 nomenon of phosphorescence is observed at 0, or even at a 

 lower temperature. On a cold night the colonies on a plate 



