The placenta is permeable to B12Co60. Together with salts, sugar, amino acids, vitamins, and proteins, the B12 is contributed to the growing embryos from the mother's body stores. At birth, the placenta contains a liberal amount of B12, which the mother regains by ingestion of the placentas.

Nursing draws a liberal amount of B12Co60 from the mother's stores and contributes it to the body of the pups where it is absorbed and distributed in the various organs, much as noted when adult dogs are injected with B12Co60. A redistribution is noted as the months pass; but the high values in the heart, liver, and gastric mucosa persist, and the brain usually shows a slow increase.

Enterohepatic circulation of B12 may involve bile and enteric content plus hepatic, gastric, and pancreatic epithelial secretion. This type of body recycling of radioactive B12 is discussed but not proven.

High values of B12 in the heart, brain, gastric mucosa, and liver indicate that the vitamin is functionally active, not an inert fraction.

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