[Among the hundred patients who formed the basis of the inquiries mentioned in this work, forty-one accused external cold of producing the attack, but many of these produced insufficient evidence that such was the case.] In short, the direct effects of atmospheric cold would seem to be these. Mere lowness of temperature goes for something, but not much; [The most marked instance of the effect of cold, _per se_, that I have seen, was exhibited by a young lady who was under my care during the past severe winter (1870-'71). During much of the time she was confined to a carefully-warmed apartment, on penalty of a violent paroxysm if she left it.] for about as much, perhaps, as it does in the way of aggravating all neurotic tendencies. Cold joined with wind is much more powerful. And the maximum of ill-effect seems reached by very cold wind mingled with sleet or driving rain, which keeps the skin sodden. But the conclusion at which I long ago arrived is, that none of these influences ever take more than a small (though it is sometimes an important) part in the production of neuralgia; and that in the majority of cases there is no pretence for supposing that they had the slightest share in its causation. A word or two must be said as to the _modus operandi_ of cold and cold wind, as these are the most frequent of external, so-called "exciting" causes. The popular use of such phrases as the latter has an extraordinary influence in disguising the plain fact, which is, that these influences operate wholly in the direction of robbing the nerves of force. The continuous abstraction of heat from the surface, which of course is materially aided by rapid movement of the air, must necessitate a readjustment of the distribution of energy, the only result of which must be to drain the sensory nervous centre of its reserve of force. But, in fact, there is an experiment, ready performed to our hands, which may amply satisfy us as to the kind of influence exerted by cold on superficial nerves, viz., the sensations experienced in recovering from frost-bite, which has been severe enough to paralyze the nerves without causing actual gangrene of the tissues. The passage of the nerves back from temporary death to full functional life is marked by a half-way stage in which there is agonizing pain. 4. We must next consider the effects of a class of peripheral influences which act, where they exist, in a more constant manner than any others; viz., those in which the trunk or periphery of a sensory nerve either receives a severe injury, or becomes more or less engaged in inflammatory processes, or compressed or otherwise damaged by the growth of tumors or the spread of destructive ulcerations.