ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 427 



Solution 1. 



Crystallized sodium phosphate 

 Calcium chloride 

 Syrup of iron chloride . 

 Strong hydrochloric acid 

 Water .... 



Solution 2. 



Crystallized magnesium sulphate 

 „ sodium sulphate 



„ potassium nitrate 



Common salt (sodium chloride) 



Potassium bromide 



Potassium iodide . 



Water .... 



Solution 3. 



Crystallized sodium carbonate 

 Water .... 



Solution 4. 



Well-washed, precipitated calcium silicate 

 Water 



All the salts employed must be chemically pure. Three cc. of each 

 of these liquids are added to 1000 cc. of fresh water or sea-water 

 (according to circumstances), and the whole sterilized. In his earlier 

 work Houghton Gill added a sterilized infusion of grass or of diatoms, 

 but it is not clear from the accounts whether this was still employed 

 with the above solutions. We have obtained very good cultures with 

 the above solutions, to which we did not add any organic infusion. 



3 (a). Modification of MiqueVs method. " Miquel Sea-vjater." 

 Since several of the components in Miquel's formula for solution A 

 (p. 423) are obviously unnecessary, when sea-water is being used as 

 the basis of the culture-medium, we adopted for our own work the 

 following modifications : — After some preliminary experiments it was 

 found, as would be expected from the composition of sea-water, that 

 the only salts of value to the medium are the three nitrates, KNOo, 

 NaNOo, NH^NOg, and possibly KBr and KI. The omission of 

 the two latter was soon found to make no difference. Experiments 

 also showed that the formula for solution A could, without any 

 appreciable detriment to results, be further simplified to the one 

 salt, KNOg, or XaNO^, but not NH^NOo. At first the amount of 

 KNOg, dissolved in 100 cc. distilled water, used to make the modified 

 solution A, was the same as the sum of the weights of the nitrates in 



