Macleod pointed out that many eminent scientists had tried to isolate this hormone and failed, without obtaining any conclusive evidence of the existence of an internal secretion (17).
Their work with duct-ligated dogs had been unnecessary, but they had gained knowledge without which they might never have developed the skill and insight to get the internal secretion from an easier source.
There could never be a practical clinical application of the internal secretion of the pancreas unless they could come up with a better way of obtaining pancreatic extract.
Therefore, the fetal pancreas might be a practical source of an extract rich in internal secretion but free from the destructive enzymes of pancreatic juice.
