This explains the phenomena of the mathematical exactness with which the minimum daily need can be estimated under experimental conditions, and with which doses less than the amount of actual body need relieve existing withdrawal signs in definite proportion to the amount of opiate administered. In exact proportion as the drug of addiction is present in the body to neutralize or oppose some antidotal poison, is the patient free from withdrawal symptoms and from physical craving for the narcotic drug. The development and existence of such mechanism in the body of the opiate addict is suggested also by the apparent continuance of tolerance to opiate existing after long periods without drug in individuals who had previously suffered from addiction-disease, and in the susceptibility of the former sufferer subsequent to the arrest of his physical need for opiate, to the re-establishment of that need by the subsequent administration of the drug. Illustrative of this phenomenon is a case who, after about two years of relief from addiction-disease, developed pneumonia and to whom in delirium and threatened death, opiates were administered as unavoidable medication. After cessation of his delirium, he was dismayed to discover addiction-manifestations and body-need for opiate drug had been re-established. This history is one of a number in my possession, and has been verified. The case demonstrating the longest persistence of susceptibility among my records, is that of a man in the early fifties who underwent an emergency operation for infected gall-bladder. A day or two following operation he developed excruciating pain in his right side just under the ribs. It had been necessary to administer opiates since a day or two before the operation. I was called in consultation for the purpose of determining the character and origin of the pain, and diagnosed a pleurisy, the pain of which subsided on the following day. Opiates were discontinued with a result of precipitating unmistakable withdrawal phenomena. To his great anger and surprise, I accused the patient of being an opiate addict. He indignantly declared that he had never used opiates in his life. Subsequent investigation with the aid of older members of his family disclosed a distinct and typical history of addiction manifestations following opiate administration in the course of treatment of a complicated fracture of his thigh in early boyhood. The drug had been withdrawn at that time and the addiction manifestations finally disappeared, he never having been aware of the facts. His reawakened addiction-manifestations were easily and quickly checked.