INTRODUCTION 7 



ophyllous euglenoids and tlieir colorless, and, in some genera, 

 phagotrophic (i.e. particle-ingesting) relatives. These interrelated 

 investigations are not mentioned merely to indicate the demands 

 made by a phycological problem on academic curricula: they 

 indicate the variety of points of view needed in cell physiology 

 and cancer research. 



One index of the advance of biochemistry is the rate of identi- 

 fication of new metabolites. Many important compounds first 

 came to notice as vitamins for animals or microorganisms. There 

 are indications that we are coming to the point where all the 

 vitamins for the rat or mouse are known; avian nutrition may 

 not be far behind. In the future, therefore, a much greater reli- 

 ance will have to be placed on microorganisms (and probably 

 on tissue cultures also) to reveal new metabolites by means of 

 their functions as growth factors. It is quite likely that specialized 

 cells when grown in tissue culture may require growth factors 

 not required by so relatively hardy and undifferentiated a cell 

 type as the fibroblast. Media for tissue culture are already for- 

 midably complex, as are also those for many of the microorgan- 

 isms (e.g. lactic acid bacteria) used for assay purposes. The algae 

 promise to be a recruiting ground for an endless series of guides 

 to yet-to-be-discovered metabolites and to more adequate methods 

 of quantitative estimation of already identified cogs in the cell 

 machine. 



Algae as Biochemical Reagents 



One method of isolating algae is to use mineral agar to ex- 

 clude heterotrophic organisms. This procedure also suppresses 

 algae with heterotrophic requirements (such algae may still ob- 

 tain the bulk of their carbon by the reduction of CO2). In con- 

 trast, algae isolated by the washing procedure (Pringsheim, 

 1946) have an opportunity to exhibit growth factor requirements. 

 The prevailing impression that most algae do not need growth 

 factors may prove to be erroneous: the condition found in the 

 euglenoids, where growth factor requirements have been demon- 

 strated in all adequately studied strains, may represent a common 

 condition in other groups. In Euglena gracilis, the simplicity of 



