442 ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 



cultures were kept under observation for at least four months. Series. 

 were made as uniformly as possible, and controls in standard media 

 were included in each. The strength of the various solutions used in 

 these experiments was the same as in Miquel's formula. 



A. Outside water + .sol. A + sol. B (normal Miquel sea- water). 



First control. 



B. Outside water + sol. A + NaoHPO^ sol. + FeClg sol. + CaCl.^, .sol. 



Second control. 



Good normal cultures were always obtained in these two controls. 



C. Outside water + sol. A + ISra2HP0^ sol. 



A very uncertain medium. Sometimes no growth has been 

 recorded and at other times a fair growth results, but these 

 cultures are never equal to normal jNIiquel. 



D. Outside water + sol. A + FeClg sol. 



Occasionally a very small growth has been obtained, but at the 

 best it is very poor. 



E. Outside water + sol. A + CaCU sol. 



About equal to D. 



F. Outside water + sol. A + Na^HPO^ sol. + FeClg sol. 



Uncertain as C ; no cultures have been obtained equal to tlie best 

 inC. 



G. Outside water + sol. A + Na^HPO^ sol. +CaC1.2 sol. 



Some cultures very nearly equal to the controls have been obtained 

 in this medium. 

 H. Outside water + sol. A + FeCI, sol. + CaCl._> sol. 

 Poor, about equal to D. 



Analysing the above results, we see that — 



(1) None of these modifications of sol. B give results equal to sol. B 



itself. 



(2) The best result is obtained from the combination of the phosphate- 



and calcium chloride solutions. 



(3) Of the solutions used singly the phosphate is the best, the iron and 



calcium chloride being about equal. 



(4) The addition of FeCl3 to Na.^HPO^, or the addition to CaCl, to 



FeClg, does not improve the medium to any extent. 



Experiments were also made to determine whether the precipitate 

 thrown down in sea-water by Miquel's sol. B, itself had any influence 

 on culture media. A quantity of this precipitate was prepared, filtered 

 ofi', and then added to outside sea-water + sol A (nitrates). A small 

 growth was obtained, which was a distinct improvement on the control 

 without the precipitate, but exhaustion soon set in. 



Further discussion of the mode of action of sol. B, and as to 

 whether that action is purely nutritive, or partly nutritive and partly 



