The nature of the action of insulin in producing cure in cases of schizophrenia is still quite obscure. One of the most striking features of insulin hypoglycaemia is the occurrence of phenomena pointing to disturbance of the autonomic nervous system, and many authors on this subject have expressed the belief that insulin produces cure by virtue of its action on the autonomic nervous system. There is, however, extensive contradiction in the literature as to what actually are the changes which take place in autonomic functions during hypoglycaemia. Some authors say that hypoglycaemia produces a generalized sympathetic stimulation, some say a generalized parasympathetic activity and others that there is dissociation of action of the two systems. Sakel (1) appears to believe that hypoglycaemia produces a vagotonia which underlies the curative effects of his treatment; Hadorn (2), that small doses of insulin stimulate the vagus, and large doses cause a primary secretion of adrenaline; Beno (3), that changes on the vegetative system cannot be sufficient to allow a reasonable understanding of the results; Pfister (4), that hypoglycaemia produces beneficial effects in schizophrenia because it damps the sympathetic; Wespi (5), that dissociation appears to prevail in the autonomic regulation; Gellhorn (6), that the treatment is successful because it leads to excitation of the sympathetico-adrenal apparatus through hypoglycaemia of the brain; and lastly, Heilbrunn (7), that his experiments are in favour of a sympatheticotonia.