ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 379 



circulatiou, without very considerable expense. Experiments 

 on a small scale, which we were able to make, unfortunately 

 only with imperfect apparatus, showed that Avater treated with 

 ozonised oxygen gave distinctly better cultures than untreated 

 water. Although the sea-water was not absolutely sterilised 

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

 of water which was visibly clouded with bacteria became 

 quite clear and bright. 



(f) Cultures in these Media. — 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, Skeleto- 

 nema, or Ch as toe eras. 



A. " Outside water" untreated. 



Small growth in from five to fifteen days, almost 

 immediately swamped by growths of foreign forms ; 

 the latter, however, will never be large. 



B. Ditto, sterilised. 



Slightly larger growth, very soon becoming ex- 

 hausted, 

 c. "Tank-water" untreated. 



Same result as in a, but growths will be much larger 

 and healthier, and will last longer. 



D. "Tank-water " sterilised. 



A fair growth of the inoculated species, but the total 

 growth will not be as great as in c ; the diatoms will 

 retain their normal appearance for some time. 



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



Best culture in series, both in quantity and quality. 



The diatoms will remain normal and healthy for a 



very long period, 

 r. " Outside water " sterilised and treated with animal 



charcoal. 

 Fair growth, especially at first; diatoms will soon grow 



pale and become exhausted ; better than n. 



