ARTIFICIAL CULTURE OF IMARTNE I'LANKTOX ORGANI81MS. 389 



(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 additiou of FeCl.^ to Na^HPOj, or the addition of 

 CaCljto FeCl.., 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 solution B, 

 itself had any influence on culture media. A quantity of this 

 precipitate was prepared, filtered off, and then added t(j 

 outside sea-water + solution 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 solution B, 

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

 nutritive and partly protective, is better postponed until a 

 later section, after the action of animal charcoal and other 

 substances has been considered (see p. 405). 



Animal Charcoal and Peroxide of Hydrogen. — The 

 most successful culture medium for plankton diatoms, next 

 to Miquel sea-water, is that prepared from animal charcoal 

 (cf. p. 379). Animal charcoal water gives at first almost 

 as good cultures of plankton diatoms as Miquel sea-water, 

 but the tendency to paleness and exhaustion appears much 

 sooner. The best cultures were obtained in "Berkefeld 

 water,'^ that is, tank-water from the Plymouth Aquarium 

 treated with powdered commercial animal charcoal and filtered 

 through a Berkefeld filter. Tank-water as a basis for animal 

 charcoal water is very much better than outside water, 

 probably on account of the higher concentration of nitrates, 

 etc. 



There is a very striking resemblance between the effect of 

 animal charcoal and of Miquel's solution B upon sea-water 

 used for diatom cultures, and the growths obtained by using 

 tank-water + solution B and tank animal-charcoal water are 

 very similar in character. If Miquel's solution A is added to 

 animal-charcoal water there is a great improvement, both in 



