Securing Food 31 



According to Sachs (1928), elements occurring in small amounts in 

 the sea may be present as impurities in the salts even in excess of their 

 concentration in natural seawater. The two formulae generally used in 

 Germany are given in Tables 6 and 7. 



Sodium chloride and calcium sulphate are dissolved first in about 

 30 liters of water. The solution is vigorously shaken and stirred until 

 all the calcium goes into solution, then the other salts are added and 

 the volume is made up to 100 liters. If the water is very hard a smaller 

 amount of calcium sulphate may be used. 



table 7. Schmalz's formula for making larger quantities of 



artificial seawater. 



Sodium chloride (NaCl) 2815 gm. 



Potassium chloride (KC1) 67 gm. 



Magnesium chloride (MgClo 6 HoO) 551 gm. 



Magnesium sulphate (MgSO-i 7 HoO) 692 gm. 



Calcium chloride (CaClo HoO) 145 gm. 



Water 1 00 liters 



First dissolve all the salts excepting calcium chloride; bring up the 

 solution almost to 100 liters; then add calcium chloride and water to 

 make up the volume. 



Before using, the newly prepared solution should be tested on sea 

 anemones or other organisms. 



METHODS OF SECURING FOOD FOR MARINE 

 INVERTEBRATES 



No culture of any organism may be maintained for a long period 

 if proper food is not regularly supplied. In the case of carnivorous 

 animals the problem resolves itself into ascertaining the forms which 

 constitute the principal food of the animal in question and in finding the 

 means of keeping a good supply. Thus many organisms subsisting on 

 animal plankton may be maintained for a long time if an arrangement 

 is possible by which regular plankton samples may be taken and the 

 desired forms obtained. Copepods or other planktonic crustaceans may 

 easily be segregated from the mass of algae and other micro-organisms 

 with which they are closely associated, by pouring the sample of plank- 

 ton into a crystallizing dish about 10 inches in diameter and from 3 to 

 4 inches high, the outside wall of which is painted black with the excep- 

 tion of one vertical strip about one inch wide which should remain un- 

 covered. A short time after the dish has been placed on a laboratory 

 table with the open space toward the light, copepods and other crusta- 

 ceans congregate at the two opposite sides depending upon the photo- 

 tropic reactions which control their behavior. They may easily be re- 

 moved with a pipette and fed to the animals in the tanks. 



