Usually nausea, or a feeling of sickness, precedes vomiting. Vast amounts of research have been devoted to study of the mechanism of vomiting. We know now that it is intimately connected with the whole nervous system. Any severe pain can bring on these symptoms, such as a sharp blow in the center of the abdomen, or bruising of the male sex glands. Disagreeable sights, odors or tastes, or, in sensitive people, even thinking of disagreeable incidents may set up the reaction. The old novels about delicate young ladies tell of the girl who comes home after a disagreeable social evening and gets quite sick thinking about it. Vomiting can result from the action of drugs. Painful sensations coming from the urinary tract, as by the passing of a stone, can set up this series of reactions.
Sometimes vomiting occurs without any preliminary warning of nausea, particularly when there is increased pressure inside the skull. Vomiting occurs in diabetic acidosis, in congestive heart failure, in cases of insufficient oxygen to the brain, in air sickness and sea sickness or other conditions that disturb the sense of balance or equilibrium.
Obviously the doctor has to find out promptly why any one vomits. He has to rule out the beginning of acute infectious diseases, and then make sure there is no acute surgical emergency like an inflamed appendix or gall bladder or peritonitis or obstruction of the bowel.
Severe indigestion, high blood pressure, pregnancy in women, disorders of the nervous system, drugs and poisons are other possible sources of difficulty in holding down food and water. Severe emotional upsets must be investigated. Finally come such rare and extraordinary problems as cancer, uremia, diabetes, and many more.