Three years later,
Castle established that gastric acid contains an ‘‘intrinsic
factor’’ that combines with an ‘‘extrinsic factor’’ to allow
this latter to be absorbed.3 Hodgkin later identified the
structure of vitamin B12, for which he received the Nobel
prize.4 Years later, in 1948, Herbert discovered the structure
of folic acid and described its association with the aetiology
of megaloblastic anaemia.