_Banting’s idea._--Thus the subject stood when, in the autumn of 1920, Frederick Banting, recently home from the war, began his work. The idea came, he writes, while reading an article dealing with the relation of the islands of Langerhans to diabetes. In his own words, it was this: “From the passage in this article, which gives a resumé of degenerative changes in the acini (cells connected with the ducts or passageway system) of the pancreas following ligation of the ducts, the idea presented itself that since the acinous, but not the islet tissue, degenerates after this operation, advantage might be taken of this fact to prepare an active extract of islet tissue. The subsidiary hypothesis was that trypsinogen (one of the digestive ferments prepared by the acinous cells) or its derivatives was antagonistic to the internal secretion of the gland. The failures of other investigators in this much worked field were thus accounted for.” In other words, the failure of his predecessors, Banting thought, was due to the probability that the digestive juices of the pancreas destroyed insulin before it could be extracted from the islands, and his plan was to circumvent this difficulty by first destroying the part of the pancreas concerned in making these juices. _The first insulin._--Banting took his idea to Professor Macleod of the University of Toronto. He received encouragement and facilities for work, and in the laboratory of Professor Macleod, with the skilled assistance of Mr. C. H. Best, he put the idea to the test, and it worked. Dogs made diabetic by removing their pancreas were treated with material obtained from degenerated pancreas, and could be kept alive. The sugar in their blood decreased each time this material was injected beneath the skin and the sugar in their urines diminished. This was the first insulin. The next step was taken soon after. Banting and Best knew from the work of their predecessors that the pancreas of animals in the womb, that is, of embryos or fetuses, show island tissue some time in their development before the tissue responsible for the digestive juices is fully formed. It occurred to them, therefore, that they could circumvent the destructive action of the juices by making insulin from embryo calves. This was tried, and it succeeded. Enough insulin was obtained to try on a patient. Later developments permitted the preparation of insulin from adult animals. Swine and beef pancreas from the slaughter house became the source of insulin. At first these preparations contained some protein which made it poisonous, and unsuitable for use in patients. Another chemist in the University of Toronto, Professor J. B. Collip, overcame this difficulty, and, with the co-operation of a group of able physicians in the university, Doctors Graham, Campbell and Fletcher, the new insulin was used on a large group of patients, and its value thus became definitely established.