Vitamin B 12 Assay in Body Fluids using Euglena gracilis

The methods of assay of vitamin B12 most generally used depend on the fact that some lacto- bacilli require this vitamin as an essential growth factor and that growth is proportional to the amount available over a certain range of concentration. Some desoxynucleotides (Shive, Sibley, and Rogers, 1951), desoxyribonucleosides and thymidine particularly, and many other substances too, have, however, been found to replace vitamin B12, although in relatively large amounts only.