AQUATIC ORGANISMS AND EXTERNAL METABOLITES 505 



As to the suggestion that the hypothesis visuahzes too many 

 potent influences, they are not Hkely to be equipotent; as In the 

 body some will prove of major potency and others significant but 

 relatively minor. It is the first two criticisms which are the most 

 cogent, although to some extent the points just made for B12 are 

 relevant to the first — as to whether significant quantities are 

 found In nature to meet the postulated needs — just as the known 

 facts about the harmful effects of certain dinoflagellate toxins 

 in nature are relevant. As to the suggestion that some undoubtedly 

 potent metabolites might speedily be changed chemically after 

 release, in so far as our Increasing knowledge only serves to con- 

 firm the idea of the sea as a veritable witches' brew, so It may well 

 be! The secondary product, however, may be no less significant. 

 These criticisms are, in fact, more relevant to the difficulties of 

 imitating in vitro the conditions in vivo. Experiment classically 

 demands the simplicity of a minimum number of variables, for 

 example, bacteria-free algae, while In nature communities are 

 usually complex, and a bacteria-free diatom probably does not 

 exist! At present, even when we have valuable hints from the 

 laboratory, all too often we are entitled to conclude only that those 

 or related processes may occur in nature sometimes and somewhat, 

 and the vital questions remain as to how often and how much. 

 We have only to think for a moment of the enormous labor In- 

 volved in answering some of these questions, even when we have 

 evolved all the necessary assay processes, to see how essential It 

 is to select carefully the most useful processes for Investigation. If, 

 therefore, we are reasonably convinced of the value of such work 

 it may be useful to review possible lines of Investigation. 



1. From many points of view, the culture of microorganisms 

 comes first. It is from the early attempts to grow plankton algae, so 

 ably followed by workers such as Provasoll and Droop, that some 

 of our best clues have come, and others will follow. Even in this 

 best investigated field there is still much to be done in evolving 

 precise culture media for algae, and particularly for some of the 

 more or less oceanic diatoms and dinoflagellates which have so 

 tempted us and defeated us In the past. Some clues in this field 



