It has been recognized in recent years that the only climates which give reasonable hope of being helpful for the tuberculous are those which present a variation of some thirty degrees in their temperature every day. Whenever this is the case chilly feelings are always produced in those who are exposed to the change, even though the lower temperature curve may not go down to anywhere near freezing. If for instance the temperature at the hottest hour of the day, say three o'clock in the afternoon, is 90° F. and that of the later evening or middle of the night is 60° F., chilly feelings will be produced. Just the same thing is true if the temperature is between 30° F. and 40° F. shortly after the middle of the day and then goes down to {181} near zero at night. These chilly feelings are uncomfortable, but they produce an excellent reaction in the circulation and set the blood coursing from the heart to the tissues better than any medicine that we have. In the midst of this the lungs have their resistive vitality raised so as to throw off the disease. This is probably one of the principal reasons why mountain climates have been found so much more helpful for the treatment of tuberculosis than regions of lower elevations. Whenever the elevation is more than fifteen hundred feet there will almost invariably be a variation of thirty degrees between the day and the night temperature. There are of course still greater variations, even sixty or seventy degrees sometimes where the altitudes are very high, but this is often too great for the tuberculous patients to react properly to, in their rundown conditions. Besides, the air is much rarer at the higher elevations, breathing is more difficult, because the lungs have to breathe more rapidly and more deeply in order to secure the amount of oxygen that is needed for bodily necessities from the rarified air. The middle elevations then, between fifteen hundred and twenty-five {182} hundred feet, have been found the best for tuberculosis patients, and they are very pleasant during the summer time, though never without the chilly discomfort of the drop in temperature. During the fall and winter, however, many patients become tired out trying to react to these variations of temperature and want to seek other climates where they will not have to submit to the discomfort and the chilly feelings. If they come down to more comfortable quarters before their tuberculosis has been brought to a standstill by the increase of their resistive vitality, it is very probable that they will lose most of the benefit that they derived from their mountain experience. Here is where the will comes in. Those who have the will to do it and the persistence to stick at it and the character that keeps them in good humor in spite of the discouraging circumstances which almost inevitably develop from time to time, will almost without exception recover from their tuberculosis with comparatively little difficulty,