428 ON THE AKTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 



Miqiiel's own formula,, viz. 5 grm. But later experiments showed 

 that a considerably greater concentration of KNO3 than this gave 

 more lasting cultures ; the strength of solution, and amount to be 

 added to a litre of sea-water, in order to obtain the best results, being 

 2 cc, 2M, KNO3. 



In the case of solution B no modification has been adopted, but it 

 has been found that small variations in the amounts of the ingredients 

 used do not affect the results. A convenient method for measuring 

 the right amount of FeClg is to warm the salt until it just melts in 

 its own water of crystallization, and to pipette out 2 cc. with a 

 previously warmed pipette. No temperature corrections need be con- 

 sidered. Also 2 cc. of the ordinary pure concentrated hydrochloric 

 acid at room temperature will suffice. 



Our own formula for preparing Miquel sea-water is now : — 



Solution A.* 



Potassium nitrate .... 

 Distilled Avater .... 



Solution B.f 



Sodium phosphate (N'a2HP04l2HoO) 

 Calcium chloride (CaCUBHoO) . 

 Ferric chloride (melted) , 

 Hydrochloric acid (pure, concentrated) 

 Distilled water .... 



To eacli 1000 cc. of sea-water:|: add 2 cc. solution A and 1 cc. 

 solution B, and sterilize by heating to 70' C. AVhen cool, decant off 

 the clear liquids from the precipitate, which will have formed when 

 solution B is added to the sea-water. 



As a rule our cultures were made in 60 cc. of this medium, con- 

 tained in short-necked, wide-mouthed flasks of 125 cc. capacity, so 

 that the proportion of air-surface to volume of liquid was large. 



The medium was found to give constantly satisfactory results. On 

 inoculation from a persistent culture of such diatoms as Thalassiosira, 

 Skeletonema, Chaetoceras, etc., a growth visible to the eye is obtained in 

 about ten days, and then multiplication takes place very rapidly. In 

 from three weeks to a month's time a very considerable growth will 

 be seen making a brown, flocculent mass at the bottom and back of 

 the vessel containing the culture. 



* This strength has only been used in the most recent experiments ; and solution A in 

 this paper, unless otherwise stated, means the iive per cent solution of KNO,. 



t For preparing this solution see p. 423. 



J " Miquel water " seems to succeed equally well, whether it is made by adding Mi(iuers 

 solutions to " outside water'' or to " tank water" (cf. p. 437). 



