Dysmenorrhoea, a painful menstruation, when not dependent on a purely mechanical cause, affords a strong example of neuralgia connected with sexual difficulty; but there is every reason to think that the neuralgia is the primary and not the secondary affection. The only effective prophylaxis, therefore, is the adoption of such general measures as will raise the whole tone of nervous health. It often happens that marriage completely cures the tendency to these attacks. (5) Insufficiency and irregularity as to the allowance of sleep are potent influences in developing neuralgia in those who are hereditarily predisposed. It is needless to say a single word to prove the imperative need of the young for periodical and prolonged repose from the conscious actions of the nervous system. Full ten hours of sleep in the twenty-four, for boys and girls who are at or near the period of puberty, is an absolute necessity if we would prevent any existing irritability of the nervous system from developing into the fully-formed neurotic temperament. Indeed, I believe that, for all young people (but especially girls) up to the age of twenty-five, this allowance is not the least beyond what is necessary: only the need is most pressing at, and just before, the development of the sexual organs. Of course a much larger allowance of sleep is necessary in actual infancy: from seven to twelve we may be content if we get nine hours clear sleep; but during the two or three years preceding puberty we should insist upon ten hours, at any rate for children who possess the nervous temperament. (6) Impurity of the atmosphere in which they habitually or daily reside must be carefully shunned for young children, especially for the nervous. The kind of dull and diffused headache which children often complain of, after study for some time in a close, ill-ventilated school-room, is very likely (if the bad influence be continued for a number of years) to develop itself, at puberty, into a regular migraine. Purity of air in the school-room must therefore be scrupulously provided for; and the same thing must be attended to as regards the sleeping rooms. Of the climatic influences we may speak in a few words. Besides the avoidance of distinctly malarial districts, and also of places where, although there is no distinct ague, there is a prevalence of neuralgic or even of so-called "rheumatic" complaints, it is necessary very carefully to shun damp soils, and places where there is a great deal of harsh and cold wind. Mere lowness of average temperature is not in itself a strong predisposer to neuralgia, at any rate if guarded against by abundant food and the use of such clothes as will prevent children from ever feeling chilly and depressed. But damp and harsh winds are actively bad; and when joined to habitual or frequent lowness of temperature, they constitute very unfavorable surroundings for the nervous systems of delicate children.