A great deal of confusion has arisen from the use of the term "shock." Conditions that are probably little related to one another are classified together under this general heading. Several recent workers have suggested other terms in an endeavor to lessen the misunderstanding. Until the factors that are responsible for the decline in the volume of circulating blood and the drop in the blood pressure are better understood, it would probably be advisable to designate the initiating agent as, for example, shock following trauma to an extremity, shock following burns, or shock following injury to the central nervous system. Shock resulting from injury may be roughly divided into two types: (1) primary shock, in which a low blood pressure follows immediately, and (2) secondary shock, in which at least an hour usually elapses between the time of injury and the development of a low blood pressure. It is the