The balance of the vagus and sympathetic parts of the vegetative nervous system is influenced by the action of morphine, as is well seen in the contraction of the pupil. The chief function of the vegetative nervous system is its control over smooth, or involuntary, muscle as is found in the pupil, the stomach, the intestines, the heart, etc. In a study of the smooth muscle reaction of the stomach and large intestine as a means of estimation of the vagus-sympathetic balance of the vegetative nervous system, we found that the gastro-intestinal smooth muscle, as viewed by the roentgen ray, could be used as an index or criterion, and this we have called the smooth muscle reaction.1 Blood pressure effects are also expressions of the influence of the vegetative nervous system on smooth, or involuntary, muscle.
In this research, a number of drugs, gland extracts and salts were studied;
LUDLUM SD, McDONALD E. MORPHINE HUNGER AND THE SMOOTH MUSCLE REACTIONA STUDY OF THE HABITUÉ. JAMA. 1926;86(12):835. doi:10.1001/jama.1926.02670380025011