METHODS OF OCEANOGRAPHICAL RESEARCH 269 



from the sea near Plymouth. It was thought that this 

 represented a true picture of the density of population 

 until an ingenious laboratory method for counting the 

 organisms present was devised. In the laboratory half 

 a cubic centimetre of water taken from the sea was added 

 to a large volume of sterilized sea water. This large 

 volume was then divided into seventy parts, each of which 

 was put into a separate flask. These seventy flasks were 

 then allowed to stand for several days, and on examination 

 it was found that " cultures " of various organisms had 

 grown in them. On the assumption that each culture of 

 each species must have sprung from at least one individual 

 of its kind, which must have been present in the original 

 half cubic centimetre, it was found that the original 

 number of organisms present in the sea water was at least 

 464 per cubic centimetre — a considerable advance on the 

 fourteen found by the centrifuge method, which was 

 evidently not fully efficient. 



