Shock has been defined by Gould as "the depression or grave effect produced by severe injuries, operations, or strong emotions; a relaxation or abolition of the sustaining and controlling influence which the nervous system exercises over the vital organic functions of the body. It is the result of a profound impression made on the cerebrospinal axis, either directly through the agency of an afferent nerve, or through the circulation." Some authors consider shock to be a paralysis or weakening

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... the vasomotor center in the medulla, caused, reflexly, by a disturbance of the sensory nerves. As a result of this weakening of the center there follows a diminution of the tone of the blood-vessels, a weakening of the propelling force, and as a consequence the blood tends to collect in the veins, particularly those of the abdomen. There is a lowering of arterial tension and probably an anemia of the brain and lungs. The causes of the shock of operations are not thoroughly understood. Prolonged anesthesia and exposure of the patient to cold, excessive loss of blood, and much handling and exposure of the abdominal viscera seem to be the chief causes of shock. The condition of the patient also plays an important part in shock. The seat of operation is likewise an important factor, operations on the liver, gall-bladder, and duodenum being most apt to cause it. It is noticealjle in extensive hysterectomies. The time when shock occurs is usually during the operation or within a few hours immediately following it. Many surgeons think that shock may come on several days after operation. This "delayed shock" is very rarely, if ever, seen following surgical operations. The symptoms in these cases are probably due to other things, such as hemorrhage, sepsis, tympanites, embolism, etc.