528 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY 



down the rope from the surface. The water required for 

 the centrifugal investigation is taken from the water 

 bottle, received in glass-stoppered bottles and placed in a 

 cool and suitable place until the laboratory is reached : 

 the examination should take place as soon as possible 

 after the catch is made. 



The employment of the centrifuge 

 for this work was first suggested by 

 Cori (6). but it has not been much 

 ,| used, as it was pointed out that the 



Jy j BL action on various organisms is selec- 



&tik JB Jl ^ive, and the sediment is therefore not 



in its constitution a true sample of the 

 plankton present. This selection does 

 not come into play if the organisms 

 are dead and in a preserving fluid that 

 is lighter than water, consequently 

 Kofoid has used the method for 

 catches preserved in alcohol. Dolley 

 (16), by using a very powerful 

 centrifuge which he termed the 

 " Plankton -okrit," and which gave 

 8,000 revolutions per minute, had 

 complete success in the sedimenta- 

 tion of living plankton. Other 

 American workers, also, have used 

 this method, and have found that 

 for accuracy of determination it 

 far exceeds all other methods at 

 present employed, 

 Kofoid, however, raised the objection due to its 

 selective influence, and found that many organisms would 

 not form a sediment. One must remember that no 

 method will be accurate for all forms, and none of the 



Fig 



4. — Krummel water 

 bottle. 



