Abstract
The effects of aureomycin, terramycin, penicillin, and streptomycin on the synthesis of vitamin B12 in the gastrointestinal tract of the chick fed a vitamin B12-free diet have been studied by means of radiocobalt. Cobalt had no effect by itself but in the presence of an antibiotic resulted in a definite increase in weight. Chicks receiving antibiotics excreted more cobalt and less vitamin B12 than those without supplementation. Synthesis of vitamin B12 in the gastrointestinal tract occurs as early as the proventriculus. Both the rate and the site of synthesis are influenced by the antibiotic fed. A higher concentration of cobalt is found in the tissues of chicks not receiving antibiotics. Antibiotics appear to have no marked effect on vitamin B12 concentration in the tissues except in the blood and gall bladder. The relatively large amount of vitamin B12 in the blood of chicks not supplemented with antibiotics suggests the poor utilization of this vitamin or the synthesis of a physiologically ineffective form.
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