In meeting the uncontrollable causes of disease the special influence of season deserves particular regard. It should always be remembered that, other things being equal, during winter the body loses, during summer gains in weight. Further, it should be remembered that these changes are abrupt: that usually the loss commences, sharply, in September and lasts until April, and that the gain commences in April and lasts until September. In September, though the weather even be warm, it is right, therefore, to add to the clothing and to commence a little excess of food. In summer it is right not only to reduce the clothing, but to eat less food than in winter. IV The best means of preventing the spread of the communicable diseases is perfect and instant isolation of the affected, and removal and thorough purifying of all clothing and bedding with which the affected have come in contact. It is a vulgar error to suppose that every child must necessarily suffer from the contagious maladies, and that the risk of exposure to infection is, therefore, of little moment. The chance of infection lessens with advance of life, and that person is strongest who has never passed through a contagious malady. Against small-pox vaccination is the grand safeguard, but even vaccination ought never to prevent the isolation of those who suffer from small-pox. V The mortality from the uncontrollable causes of disease amongst persons of advanced life is best prevented by providing against sudden vicissitudes of heat and cold. The primary care is to guard against sudden change of vascular tension from exposure to heat when the blood-vessels are weakened by cold. Such exposure is the cause of nearly all the congestions which occur during winter, and which carry off the enfeebled. The sound practice is to maintain the body, at all hours and seasons, but especially during the hours of sleep, at an equable temperature. The temperature of 60° Fah. may be considered a safe standard. VI The true danger of every form of mental exercise is the addition of worry. Laborious mental exercise is healthy unless it be made anxious by necessary or unnecessary difficulties. Regular mental labour is best carried on by introducing into it some variety. New work gives time for repair better than attempt at complete rest, since the active mind finds it impossible to evade its particular work unless its activity be diverted into some new channel. During the new work a fresh portion of the brain comes into play and the overwrought seat of mental faculty is secured repose and recovery. Excessive competition in mental labour is ruinous at all ages of life. VII