ARTIFICIAL CULTUUl) OF MARFXr: PLANKTOX ORGANISMS. 885 



Good growth at first, but exhausted sooner than A. 



C. Ditto, but two and a half times amount of solution A. 



Was slower than either A or b at start, but after- 

 wards was better than a or b, and lasted lonsrer. 



D. Ditto, but five times amount of solution A. 



As c, but in greater degree. 



Considering the nature of the substance added, and its 

 already well-knawn action in plant metabolism, these results, 

 coupled with the fact that exhausted cultures can often be 

 regenerated by the simple addition of nitrates (see below, p. 

 390), are quite consistent with the assumption that solution 

 A is simply nutritive in action. The concentration of nitrates 

 in natural sea-water is so low (Brandt [47] ) that the amount 

 available in a culture of untreated water very soon becomes 

 completely exhausted, and it is this deficiency that solution A 

 probably corrects. 



Considering now the action of solution B, it must first be 

 observed that increased concentration of nitrates alone will 

 not explain the whole action of Miquel's solutions, for no 

 increase in growth is obtained when nitrates or solution A 

 only are added to sea- water. To illustrate this point an 

 account of an actual experiment may be given : — 



Inoculated with Thalassiosira decipiens: 



A. Normal Miquel sea-water. 



Good strong culture, in every way normal. 



B. Outside water sterilised. 



Small growth at first, very soon exhausted, 

 c. Ditto + solution A. 



No improvement over B. 



D. Ditto + solution B. 



Fair growth. Great improvement on b and c, but 

 exhausted considerably before A, 



E. Tank-water sterilised. 



Appreciably better than b, but growth not large. 



F. Ditto -f solution A. 



Not even as good as e. 



G. Ditto + solution B. 



