SECT. 2] 



BIOASSAY OF TRACE SUBSTANCES 



Table I 



223 



Some Properties of Naturally Occurring B i2 Vitamins. 

 (Modified from Coates and Ford, 1955.) 



a + + + denotes "fully active" (as cyanocobalamin). 



+ + denotes activity of the order of 50% that of cyanocobalamin. 



+ denotes activity of the order of 10% that of cyanocobalamin. 



— denotes activity of < 1% that of cyanocobalamin. 



b The Ochromonas response is denoted mammalian type. 

 c Brown et al. (1955). 



summarizes the times involved in the assay, the type response (see Table I) 

 and the sensitivity of the assay. 



As Table II shows, the organisms vary in the types of compounds to which 

 they respond. By judicious selection of the proper combination of organisms, 

 more or less complete characterization of the sample's vitamin B12 activity 

 may be obtained. This is, perhaps, the most complex situation in the bioassay 

 of organic micronutrients. 



Assays for vitamin B12 in the North Atlantic and northern North Sea show 

 a seasonal variation in concentration of the vitamin in surface samples. Cowey 



