ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 435 



that water treated with ozonized oxygen gave distinctly better cultures 

 than untreated water. Although the sea-water was not absolutely 

 sterilized by the treatment to which we actually subjected it, a sample 

 of water which was visibly clouded with bacteria became quite clear 

 and bright. 



(/) Cultures in these Medici. In order to make clear the different 

 results, which are obtained by using these different waters, we will 

 describe the probable result which would be got from a series of flasks 

 set up with the following media, and each inoculated with a persistent 

 culture of a true plankton diatom, such as Thalassiosira, Skeletonema, 

 or C%actoccras. 



A. " Outside water " untreated. 



Small growth in from five to fifteen days, ahiiost immediately 

 swamped by growths of foreign forms ; the latter, however, will never 

 be large. 



B. " Outside water " sterilized. 



Slightly larger growth, very soon becoming exhausted. 



C. "Tank- water" untreated. 



Same result as in A, but growths will be much larger, healthier, and 

 will last longer. 



D. " Tank-water " sterilized. 



A fair growth of the inoculated si^ecies, but the total growth will 

 not be as great as in C ; the diatoms will retain their normal appear- 

 ance for some time. 



E. " Outside water " + Miquel's solutions A and B, sterilized. 



Best culture in series, both in quantity and quality. The diatoms 

 Avill remain normal and healthy for a very long period. 



F. " Outside water " sterilized and treated with Animal Charcoal. 



Fair growth, especially at first ; diatoms will soon grow pale and 

 become exhausted ; better than D. 



G. " Tank-water " sterilized and treated with Animal Charcoal. 



As F, only growth will be slightly greater and will last considerably 

 longer. Third liest in series. 

 H. " Tank-water " treated with Animal Charcoal and filtered through Berke- 

 feld filter. 



This will usually be the second-best culture in the series, but the 

 difference between this and G will only be slight. 

 K. " Outside water " treated with HoO.. 



This will most resemble F, but will iK^t be quite so good. 

 L. " Tank-water " treated with HoO^. 



A distinct improvement over K. This medium is rather variable, 

 and in some cases the growth obtained has Iteen quite equal to F, if not 

 better. 



