8 S. H. HUTNER 



the requirements for growth apart from the B12 requirement, 

 imparts a special value to this organism as a quantitative reagent 

 for free Bi2. 



Biochemists acutely need microbiological methods (for rea- 

 sons of specificity and economy) for measuring all the forms of 

 a metabolite. With one notable exception, the microorganisms 

 now employed as quantitative reagents measure only the free 

 ("unconjugated") form of a growth factor. The ciliate protozoan 

 Tetrahymena, presumably because it has a small-scale equivalent 

 of a digestive tract, can utilize high-molecular forms of folic acid 

 and essential amino acids supplied as intact proteins. The appli- 

 cation of this type of organism to the analytical biochemistry of 

 such vital metabolites as B12, biotin, and pantothenate should 

 help elucidate their roles in the economy of the organism. Several 

 major groups of algae contain species which have chloroplasts 

 (and are probably therefore photosynthetic) and are phago- 

 trophic at the same time. Many, perhaps most, Chrysophyceae 

 display this habit, as do many marine dinoflagellates. Such algae 

 might be expected to have rather complex growth requirements. 

 In a sense, this might prove an advantage in making these re- 

 quirements the basis of assay methods: the longer the roster of 

 growth factors, the greater the variety of assays that can be done 

 with the aid of the same organism and essentially the same basal 

 medium; the most difficult stage in the development of a micro- 

 biological assay method is the provision of a basal medium com- 

 plete in all respects except for the growth factor in question. 

 Workers in this field have to keep abreast of advances in meta- 

 zoan as well as microbial nutrition; the subject of the hetero- 

 trophic nutrition of metaphyta and of cellular algae has as yet 

 contributed little that is immediately relevant to the development 

 of biochemical reagents, or, more narrowly, to the development 

 of better culture methods for non-cellular algae. 



The derangements that initiated the carcinogenic process are 

 probably of great subtlety. Ferreting out these abnormal reactions 

 will require analytical tools of corresponding delicacy. The nutri- 

 tional requirements of algae displaying saprophytic or phago- 

 trophic tendencies may, as mentioned, provide the source of some 



