228 McKenney On luminous Hacteria. 



The question then presented itself as to whether the metal or the 

 haloid was the important element, or whether both were required. If 

 other salts of sodium could replace the chloride, then the metal would 

 be the important element. If this were not the case, then the chlorine 

 ion or the entire molecule would be required. To test this I used 

 NaNO y in the place of NaCl. Not only did I get growth in such media, 

 but the light obtained with 1$, 2$, and 3$ of the salt was even more in 

 tense than when the chloride had been used. Further, the minimum 

 amount of NaNOg, like that of NaCl, was .5$. Less than this was not 

 sufficient for growth. 



The sulphate of sodium, Na^SO ? , was likewise found capable of replac 

 ing NaCl, and while the growth was fully as good as when NaCl was 

 used, still the cultures did not become luminous as soon, nor were they 

 as bright as when NaCl was used. 



In addition to the chloride, the nitrate and the sulphate of sodium, ten 

 other sodium salts were experimented with, namely: monobasic phos 

 phate, dibasic phosphate, sulphite, phospho-lactate, citrate, carbonate, 

 acid carbonate, nitrite, tartrate, and bitartrate. Of these the first five 

 when added to a 1$ peptone solution were sufficient for growth, and, 

 except the sulphite, were sufficient for luminescence. The remaining 

 five salts were found not to be able to replace NaCl. This insufficiency 

 is, however, in all probability, due to the character of the ion linked 

 with the sodium rather than to the sodium ion itself, since eight of the 

 thirteen salts of sodium investigated, when added in sufficient quantity 

 to \% peptone solution gave good growth. 



Since MgCl^ was capable of replacing NaCl, it seemed strange that the 

 closely related KC1 could not replace NaCl. In order to make sure that 

 the insufficiency of KC1 was not an osmotic one, media was made in 

 which KC1 and KNO were added to peptone in quantities isoosmotic 

 with 1, 2 and 3$ of NaCl and NaNo T , respectively. However, in no 

 case was any growth to be observed even a week after inoculation. 



Of the salts of sodium, the nitrate, chloride and sulphate are the best 

 forms in which to furnish sodium to the bacteria. When the nitrate is 

 used, a far brighter light is obtained than when any of the other salts 

 are employed. The chloride is also used to better advantage than is the 

 sulphate. The fact that the nitrate is more advantageous than the 

 chloride of sodium indicates that the sodium need can hardly be a ques 

 tion simply of adaptation to its primitive invironment. 



The Theory of Luminescence. 



At present, those who have studied the luminous bacteria may fairly 

 be said to be divided into two camps, one holding that luminescence is 

 intracellular and that it is inseparably bound up with life, while the 

 other considers it to be extracellular, and not inseparable from life that 

 it is capable of reproduction in the laboratory. Among those holding the 

 intracellular view may be mentioned Pfliiger, Beijerinck and Lehmann. 



