From a review of recent literature, and pathological study of more than 100 personal cases, the authors describe the most interesting of these "diffuse" lesions; they only recall the most common types of lesions (contusions, vascular lesions, edema and its consequences - especially on brain stem); but a more detailed description is given of less known lesions of corpus callosum, brain stem and white matter, which have a more complex pathogeny (direct physical injury, anoxia-ischaemia, edema), and which they consider to be factors which worsen or protract the coma. "Biochemical" lesions (basic myelinic protein, liberated "false" neurotransmitters) are also discussed.