McKenney On Luminous Bacteria. 227 



taining, in addition to 1$ peptone, varying quantities of each of the salts 

 in sea water. 



Since NaCl constitutes the bulk of the sea salt, it was first experi 

 mented with. To a series of flasks containing 1$ peptone in double 

 distilled water, NaCl was added in amounts of .25, .5, 1, 2, 3, 5, 10 and 

 15 per cent, respectively. Each of these flasks of peptone and NaCl 

 was inoculated with Bacillus phospJiorescens. After 18 hours, growth 

 was present in all of the media except the one containing .25$ of NaCl. 

 At no time within the course of the next ten days was any growth what 

 ever to be found in this flask. The growth in the flasks containing .5, 

 10 and 15$ of NaCl was very slight, that in the latter two being less 

 than in the first. The growth continued in the cultures with 10$ and 

 15$ of NaCl. for only a few days and then ceased entirely. Cultures 

 containing 1$, 2$ and 3$ NaCl showed a luxuriant growth, which con 

 tinued for nearly a week. In the cultures containing .5$ and 5$ NaCl, 

 growth continued for 9 or 10 days. 



While growth occurred in all except one of these peptone NaCl 

 media, in only three was any luminescence to be observed. The cul 

 tures containing 1$, 2$ and 3$ NaCl all emitted a strong light. In none 

 of the other cultures was light discernable at any time. The light in 

 these three cultures was fully as bright as when the bacteria were grown 

 in normal fish bouillon. The growth was not, however, quite as luxu 

 riant. These experiments were repeated five times and yielded the same 

 results. 



Evidently, then, a single one of the ingredients of sea salt (NaCl) is 

 sufficient for the needs of luminescence. Would any one of the other 

 salts contained in sea water or belonging to the groups of alkali or alka 

 line earth metals do just as well as NaCl? To answer this question, to 

 1$ peptone in distilled water I added the following amounts of MgCl^: 

 .1$, .25$, .5$, 1$, 2$, and 5$, respectively. In 18 hours, growth was 

 evident in all of these except the one containing but .1$ MgCW. Only 

 those cultures containing 1$ and 2$ MgCl.j, however, became luminous. 

 The light in these cultures appeared from 24 to 48 hours later than in 

 the corresponding NaCl cultures and was rather weak. 



Media in which KC1, CaCl^, NH C1, and BaCl- 2 - were employed in the 

 place of NaCl remained perfectly clear for a week after inoculation. In 

 addition to the above salts, the following were also used in the place of 

 NaCl; KNO^, K^SO T , LiNog, RbSO T , Ca(NO T )v,, and Sr(NO )*. None 

 of these were, however, even sufficient for growth of the organism the 

 media remaining perfectly clear for the week during which they were 

 observed. 



Two of the salts of sea water, NaCl and MgCl^, are evidently of prime 

 importance for the growth and light production of these bacteria, and are 

 interchangeable. Further, the optimum amount Of MgCl^ approximates 

 the optimum amount of NaCl. The remaining salts of sea-water are 

 insufficient for the needs of the photobacteria. Not only is this so, but 

 the addition of potassium or calcium salts to a peptone-NaCl medium 

 appears to retard the growth and also light production. 



