CULTURE OF PLANKTON DIATOM- THALASSIOSIRA GRAVIDA CLEVE. 419 



the 100 c.c. contained 001 grams of CuSOi OHgO. After an interval of 

 twelve minutes a fresh flask containing 100 c.c. of culture medium was 

 inoculated with 1 c.c. from the first one. In the second flask a very fine 

 growth of diatoms appeared, which was much more healthy and 

 vigorous than untreated cultures, and contained far fewer bacteria, as 

 shown by peptone-agar plates. 



Still better results were got, however, by a method which was first 

 recommended to me by Mr. D. J. Matthews, who had made use of it for 

 destroying bacteria in aquarium water. This consists in passing an 

 electric current through the sea-water between carbon poles, until a con- 

 siderable formation of hypochlorous acid has taken place and the water 

 smells strongly of chlorine. The following description of an experiment 

 will show how the method was applied in the case of the diatom cultures. 



Experiment 449. — 2| Utres of sea-water from the Laboratory tanks, 

 which had been treated with animal charcoal and filtered through a 

 Berkefeld filter, were put in a sterilized square glass jar, and an electric 

 current varying from 1-7 to 1-5 amperes was passed through it for three 

 minutes, two carbon plates* (sterilized by heating) being used as poles, 

 the plates being constantly moved as the current was passing. The 

 electrolysed water then smelt strongly of chlorine. It was allowed to stand 

 for one hour, and then 50 c.c. of it was added to a flask {x), which con- 

 tained 50 c.c. of unelectrolysed Berkpf eld water,"]* to which had been added 

 a quantity of Thalassiosira gravida from the culture which was to be 

 cleansed. 



Sixteen flasks (a-q) had previously been made ready, each containing 

 about 75 c.c. of sterile culture medium (outside sea-water treated with 

 MiqueVs solutions and boiled). After the electrolysed water had been in 

 contact with the Thalassiosira for thirty-one seconds about | c.c. from 

 flask X was added to flask a, and similar amounts were added to the 

 remaining flasks b, c, d, etc., at intervals of about ten seconds for the 

 first two minutes, and then at longer intervals until the last flask q was 

 inoculated after the Thalassiosira had been in contact with the electro- 

 lysed water for four minutes. 



In this way a series of culture flasks was obtained inoculated with 

 Thalassiosira which had been in contact with electrolysed water for vary- 

 ing times. The flasks were placed in a suitable position before a north 

 window and the diatoms allowed to develop. At the end of a week the 

 first flasks in the series {a, b, c, etc.) showed good growth, the later ones 



" Tiie size of each plate was 120 x 44 x 6 mm. 



t See Allen and Nelson, lac. cU., p. 432 [Q.J. M.S., p. 375], 



