No other subject in the realm of disorders of the central nervous system offers more immediate rewards to study or is more timely than injuries of the brain. This is particularly true at present with practically the entire world committed to war. With the emphasis now being placed on motorized and mechanized warfare, a soldier is now about as apt to sustain an injury to the head from a "traffic" accident as he is from bullets or fragments of high explosive shell, at least insofar as injuries minor enough to permit the patient to reach trained medical attendants are concerned. It is therefore apropos in this discussion of injuries of the brain to review once more that intriguing problem of the mechanism of coup-contrecoup traumatisms of the brain, once the catchword of every junior medical student but now almost completely forgotten in the rush of matters of more immediate clinical