218 



Papers from the Department of Marine Biology. 



of any bivalent ions. This is true even when the solution is changed 

 three times to remove the last traces of Ca in the solution. KCl is 

 also relatively non-toxic, although more so than NaCl. CaCl2 and 

 MgCl2 are very toxic when alone. All combinations of NaCl with the 

 other ions of sea-water sustain the bacteria well, except that they are 

 neutral media, and hence the phosphorescence is dimmed after 24 hours. 

 That pure NaCl should have so little effect on Ught-production is aston- 

 ishing when we consider its poisonous effect on other marine organisms 

 and tissues, particularly on ciliated cells. 



Table 17. — Effect of acid and alkali. 



Concentration of acid and alkali added to Mg- 



free sea-water, m/2(100 NaCl +2.2 KC1 + 



2 CaCl2) in Syracuse watch glasses. 



n/2000 HCl 



n/4000HCl 



n/8000HCl 



n/16000HCl 



n/32000HCl 



n/500 valerianic acid . . 

 n/1000 valerianic acid . 

 n/2000 valerianic acid . 

 n/4000 valerianic acid 

 n/8000 valerianic acid . 

 n/l6000 valerianic acid 



n/500 NaOH 



n/1000 NaOH 



n/2000 NaOH 



n/250 methyl amine . . . 

 n/500 methyl amine . . . 

 n/1000 methyl amine . . 

 n/2000 methyl amine . . 

 Mg-free sea-water. . . . 

 Sea-water 



Light after — 



10 min. 



Faint. 



+ 

 + 

 + 



Faint. 

 Faint. 



+ 

 + 

 + 



+ 



Faint. 

 Faint. 



4- 



+ 

 + 



1 hour. 24 hours. 



Faint. 



+ 

 + 



Faint. 



+ 

 + 



Faint. 



Faint. 



Faint. 



+ 



Faint. 

 Faint. 



+ 

 Faint. 



EFFECT OF ACIDS AND ALKALIES. 



As NaOH precipitates the Mg of an artificial sea-water, it is always 

 necessary to use Mg-free sea-water in order that the concentration 

 of NaOH may not be reduced. The acids were also added to a neutral 

 artificial Mg-free sea-water as well as the alkalies, in order to obtain 

 comparative results. Table 17 gives the results. The return of light 

 in n/1000 NaOH and n/500 methyl amine after 24 hours was possibly 

 due to neutralization of alkali through absorption of CO2. 



As was to be expected, acids and alkalies were found to prevent light 

 emission in very weak concentration, the acids in much weaker con- 

 centration than the alkalies. In fact, the bacteria are very sensitive 

 to acid and will not even phosphoresce with any brilliancy in a neutral 

 medium. 



