ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 377 



tube leading down from the bottom of a small inverted bell- 

 jar, placed some height above (in our case 14 ft., which gives 

 a pressure of ca. G lb. to the square inch inside the jar). A 

 screw pincli-cock on this connection serves as a tap. The 

 carboy containing the treated water stands just above the 

 bell-jar, and is fitted with a tightly fitting rubber bung, 

 through which two tubes pass. One is an ordinary syphon, 

 the other the only air-inlet into the carboy. This latter auto- 

 matically keeps the level of the water in the bell-jar constant, 

 by closing the air-inlet as soon as the water covers the end 

 of the tube. When filtering water the modus operandi is 

 as follows : The carboy is filled with tank water, treated, and 

 alloAved to settle as before. The Berkefeld candle,^ bung, 

 delivery tube, and connections (see fig. 1) are sterilised by 

 boiling for half an hour, and fitted into place from within. 

 (The delivery tube is shaped so that any drops of water, 

 accidentally running down outside it, do not enter the vessel 

 receiving the filti-ate ; and the jar should be large enough to 

 allow the hand to fit the filter into place without much 

 trouble.) The pinch-cock is closed, and the syphon from the 

 carboy started, whicli will automatically stop if the bung htis 

 been properly fitted. This should be watched to avoid acci- 

 dents. The pincli-cock is tben opened until the water rises 

 in the jar well above the top of the candle, but still leaving 

 some air-space. The lid can now be fitted into place and 

 screwed down. The tightness of this joint can be tested by 

 pouring a little water into the crack round the lid, and 

 observing if any bubbles are formed when the pinch-cock is 

 opened. If all is right, no bubbles will be seen, and a good 

 stream of water will flow out from the delivery tube. Our 

 apparatus will filter about 20 litres an hour, and the filtrate 

 is exceptionally bright and clear. The candle should be 

 sterilised every three or four days that the apparatus is in 

 use to avoid indirect contamination by growths of organisms 

 through the substance of the filter.- The water while passing 



^ No. 5 porcelain mount, length 8 in., diameter 2 in. 



2 See Bulloch and Craw, ' Joiirn. of Hygiene,' vi. No. 3 (1906), p. 409. 



