Persistent headache is an exceedingly grave feature, and although it may at times disappear quickly on treatment, mental clouding and alteration of the higher functions is always to be feared; not infrequently persistent headache ushers in a final and fatal encephalopathy. In such a case the headache persists, becomes more and more excruciating, the patient rapidly shows loss of mental power, and may gradually sink into a condition of delirium. On the other hand, an attack of acute delirium may suddenly supervene, commencing with sudden loss of consciousness, followed by irregular movements of all the limbs, frothing at the mouth and nose, and finally mania. Recovery is by no means uncommon, and after a sudden attack of this description the patients are entirely ignorant of the whole circumstance; they may occasionally recover powers of locomotion, and wander to long distances, unable to give an account of themselves or to remember their names, and only after a considerable time recover consciousness of their identity; but this type of case is comparatively rare. The case quoted by Mott[10] gives a typical history of mental affection due, no doubt, to lead, but partially complicated by alcohol. =The Burtonian Line.=--Much controversy has raged around the significance of the blue line on the gums to be seen in certain persons working in lead, as to whether this particularly well-marked sign is to be regarded as a diagnostic symptom of lead poisoning or not. For a long time it was regarded, and by many is still regarded, as sufficient evidence in itself to determine that a person is suffering from lead poisoning. On the other hand, those who have had considerable experience of industrial lead poisoning, particularly in the routine examination of workmen occupied in various lead industries, do not regard the occurrence of the Burtonian line as of more value than that the person showing such pigmented gums has been exposed to lead absorption. There are two kinds of Burtonian line: