that the pain of megrim is felt in the extra-cerebral arteriesthat it is an arterial colic. Such is the view of Nothnagel and Lauder Brunton. Nothnagel refers to Traube's discovery of sensory nerves in arteries and he assumes that when, as in Du Bois Reymond's case, the pain is attended by arterial constriction of the affected side it is due to contraction of the arterial wall and consequent pressure on the sensory nerves, in the same way as in intestinal colic,49 adding : " We must look for

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... pain not in the brain, or dura mater, or the bony skull, but in the sensory nerves of the meninges. " Romberg does not attempt to explain the origin of the pain in those cases of megrim in which there is dilatation instead of contraction of the vessels on the affected side, whilst Brunton is inclined to dispute the assumption that simple dilatation or simple constriction ever occurs. He believes that affected arteries are tightly contracted peripherally, but are dilated on the proximal side of the constriction, the result being that the blood is driven with great impact against the constricted part, thus causing the pain. 50 In connexion with these views a passage from Whytt is worth quoting. After pointing out that sympathy with the stomach is one of the commonest causes of headache, he states his belief that by this sympathy "the nerves chiefly of the forepart of the head suffer; and the small vessels to which they are distributed (vaso-motor nerves ?) are either affected with a continuous spasm or agitated with uncommon alternate contractions and relaxations ; in consequence of which the patient feels a pain, straightness, fulness and pulsation about the forehead and temples. "51 And again he says that headache may be caused by a viscid or acrid humour obstructing or irritating the vessels of the pericranium, cranial muscles or dura mater, as in gout or scurvy. " If for "viscid or acrid humour " one substitutes "uric acid," a remarkable likeness is seen between Whytt's view and that more recent one of Haig which attributes to this substance great powers of contracting the bloodvessels.