The terms _shock_ and _collapse_ are nearly interchangeable, but, by common consent, the latter is usually the name given to conditions that are more sudden and overwhelming. Shock may be of all degrees--from temporary faintness, from which the patient recovers within a few moments, up to a condition of vital depression which terminates fatally, there being no reaction in spite of all efforts to produce it. =Symptoms.=--These vary to a considerable extent according as the patient is or is not under a general anesthetic. The description of _types_ and _symptoms_ includes an expressionless face, pallor of the skin and mucous membranes, with corresponding coldness of the same, _i. e._, reduction of surface circulation and heat; dilated pupils, reacting slowly to light; irregularity of the heart’s action, with a weak, irregular, thready, or almost imperceptible pulse; irregular respiration, _i. e._, irregular both in rate and depth; mental inactivity and apathy; loss of voluntary muscle movement; impairment of superficial sensibility; reduction of body temperature; and nausea or actual vomiting. These at least constitute the symptoms and form the apathetic or torpid type of shock. In the so-called erethistic type (Travers) the patients are restless and excited, uncontrollable, with irregular pulse and breathing, often with dilated pupils. In a third type, described by Travers as the _delayed_, the symptoms are as above detailed, but do not appear until some hours after the cause which has produced them, which may be a concealed (internal) hemorrhage. The delayed type is also seen in those who escape serious accident with a minimum of physical harm. As shock becomes more pronounced, mental depression deepens into coma, or mental excitement subsides into it; the surface becomes colder and bathed with perspiration, and death follows. These symptoms are those generally noted, whether following injury to the head and denoting so-called concussion of the brain, loss of blood, wound of the abdomen with injury to the viscera, blows upon the testicles, gunshot wounds or other accidents which are causes of shock. They follow also after perforation of the bowel, as in typhoid fever or appendicitis; depression following the receipt of bad news, or fright, etc.; in other words, the physical condition is practically the same no matter what the exciting cause. =Diagnosis.=--Shock is mainly to be diagnosticated from fat embolism; concealed hemorrhage as well as pulmonary edema and suppression of urine are to be suspected. It is unquestionable that many patients have died of fat embolism in whom the actual cause of death has not been ascertained, yet has been ascribed to shock. (See Fat Embolism, Chapter II.)