Experiments dealing with the distribution of B12Co60 in the dog indicate that with time (9 months after administration) there is a shift in the distribution of the vitamin as compared to the short term experiments, as well as prolonged retention of the vitamin within various dog tissues.

The heart, gastric mucosa, liver, spleen, and brain show high concentrations of the isotope in long term experiments.

This distribution, in the heart for example, does not fit with an hypothetical breakdown of B12Co60 complex and storage of a physiologically inactive fraction.

Repeated periods of anemia produced by phenylhydrazine make it possible to demonstrate radioactive material in red cell stroma of dogs that have previously received vitamin B12Co60. This radioactive material must have come from other body stores, such as liver and stomach.

The high concentration of B12Co60 in the gastric mucosa suggests a relationship between it and the intrinsic factor as described by Castle.

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