Specific Gravity and Luminescence in Noctiluca, etc. 



241 



SALTS OF SEA-WATER. 



In any one of the pure salts of sea-water, made up in m/2 solution in 

 distilled water, Noctiluca ceases to give any luminous response after 2 

 hours (table 3). CaCl2 is the most toxic, no normal response being 

 given, but a constant glow for 2 minutes. KCl is least toxic, a normal 

 response being given for 2 hours. In NaCl and m MgCl2 there is a 

 normal response for an hour, and this is accompanied on first immer- 

 sion in the salt by a constant glow which soon passes off, doubtless 

 owing to some of the animals dying. In a mixture of NaCl with one 

 of the other salts, in the proportion occurring in sea-water, the normal 

 response lasts much longer than in any of the pure salts; a little under a 

 day in NaCH-KCl, and 5 days in NaCl+CaCla or NaCl+MgCla- 



Table 3. — Effect of salts of sea-icater. 



Solution (in distilled water). 



in/2 NaCl . 



m/2 KCl . . 

 in/2CaCli. 

 in/2 MgCU. 



m/2 (100 NaCl +2.2 KCl) 



m/2 (100 NaCl +2 CaCla) 



m/2 (100 NaCl+10 MgClj) 



m/2 (100 NaCl +2.2 KCl +2 CaClz) 



m/2 (100 NaCl+2.2 KCl+10 UgCh) 



m/2 (100 NaCl+2.2 KCl+2 CaCU+lO MgCl2) 



Same mixture +m/2300 NaOH 



Same mixture +m/2300 HCl 



Luminous response. 



Normal, 1 hour (poor) ; momentary con- 

 stant glow at start. '^ 



Normal 2 hours. 



Constant glow 2 minutes. 



Normal 1 hour; constant glow 10 min- 

 utes at start. ^ 



Normal, <^1 day. 



Normal, 5 days. 



Normal, 5 days. 



Normal, 5 days. 



Normal, 7 days. 



Normal, 10 days. 



Normal, 10 days. 



Constant glow 15 minutes. 



iThe constant glow at the start is doubtless due to the dying condition of some of the animals. 



in a mixture of NaCl+KCl+CaClz a normal response is given for 5 

 days, and in NaCl + KCl -l-MgCla for 7 days. With the four salts in a 

 neutral or alkaline medium (+m/2300 NaOH), the response lasted for 

 more than 10 days, when the experiment was discontinued. The 

 addition of a small amount of acid (m/2300 HCl) to the four salts 

 prohibits any normal response, causing a constant glow for 15 to 30 

 minutes. (See also under Acids.) 



These results showing the injurious effects of pure salts on the lumi- 

 nous response of Noctiluca and the improvement on balancing with other 

 salts are in agreement with the general work on the effect of balanced 

 solutions on other physiological activities. The luminous bacteria, 

 on the other hand, are independent of a balanced medium, although 

 they must, like Noctiluca, have a certain small proportion of salt in the 

 medium (E. N. Harvey, 1914). 



