INTRODUCTION
Antigenic Nature of Insulin.
—Insulin has been proved to be a complete and soluble protein, and like other proteins1 it may act as an antigen. Precipitins and complement fixation antibodies probably are formed in the susceptible organism after the injection of insulin,2 but this opinion is not universally accepted. Reagins (circulating antibodies responsible for dermal reactions) frequently can be demonstrated in persons sensitive to insulin by passive transfer.2Chemists have been unable to find any difference in the microscopic appearances, isoelectric points, solubilities and molecular formulas of crystalline insulins from such varying sources as the ox, sheep, hogs and fish.3 Some workers have maintained that the insulin derived from the pancreases of human beings, cattle, hogs, sheep, bison and dogs has an immunologic identity.4 Other immunologists have found that beef and pork insulins have antigenic activity in common and also have a "residuum of