Perhaps the most interesting of the symptoms of the insulin reaction are those related to the central nervous system. These have been well described by many authors.1At first there is a sense of weakness, a vague feeling of uneasiness. Then follow in rapid succession vertigo, ataxia, mental confusion, incoherence of speech and marked coarse tremor. Clonic spasms and even convulsions may supervene. The last stage of the reaction, if it is allowed to continue, is complete unconsciousness. Although there has been some speculation regarding the nature of these severe symptoms, very little concerning their mechanism has been established. It was thought that the "internal jugular method" developed by one of us (A. M.2a) might help to elucidate the problem. Puncture of the internal jugular vein in man was undertaken in 1927 in the hope that greater knowledge regarding intracranial activity or metabolism might thus be obtained. Simultaneous