Consumption is also prevalent, and more especially so where children live in overcrowded rooms.

During childhood the second set of teeth come out, and we have the same diseases due to dentition as when the first set were being cut - convulsions and general derangements and disturbances of the digestive system. While the second set of teeth are being cut very serious disturbances may occur to children's systems, and you must not be surprised if children are fretful and troublesome without any apparent cause at about five years of age, when their jaws contain both sets of teeth at once, with the exception of the wisdom teeth, when forty-eight teeth are growing in their jaws all at once. When you know the trouble of any little thing wrong with either of your teeth, you can easily imagine the trouble and pain it causes a child when twenty-eight permanent teeth are growing in the jaws, and displacing the twenty temporary ones.

At this time, too, the bad effects of rickets in infancy show themselves in a very marked degree. Rickets is a disease in which the bones are unable to take sufficient of the lime salts out of the blood, so that they are too soft, and one of the worst effects of this is, that when the external air presses upon the chest walls during expiration, and the lungs inside collapse, it bends the soft ribs, and so pushes the breast-bone forwards and makes the child pigeon-breasted, so that the lungs cannot expand as far as they did before; the heart is likewise impeded in its action. You see, then, that rickets is a very serious disease, and its prevention of extreme importance. You must take the words of Sir William Jenner, that it is the first of many preventible diseases, and ought to be prevented. Another evil of rickets is, that the bones of the legs of ricketty children being soft, when they walk, which they are not inclined to do, the weight of their body is too much for the soft bones in the legs, and so you have crooked-legged children.

In youth, the third period, growth is still going on: a great deal more food is required then than later on in life, and much exercise is desirable. It is not necessary to warn great numbers of the youths of this country that exercise is necessary, for sometimes it would appear to be almost worshipped, but there are great masses of people in this country who do not take a right amount of exercise. Girls, as a rule, do not take anything like as much as they ought; it has become very much more prevalent in girls' schools to make them take more exercise, and it is a very good thing; but there are numbers of young people who are engaged many hours a day, not at work which requires much bodily exercise, but at work which is called sedentary work, sitting in offices and work-rooms, and they do not feel much inclined for exercise when the day's work is over, and very often, in the time that they might devote to exercise, do many other things which are not by any means advantageous to them. It ought to be impressed upon them that they are people who, at their time of life, require bodily exercise, - I mean bodily exercise in which all their muscles are more or less brought into play. Walking to and from their business is all very well in its way, but it by no means exercises all the muscles of the body. There are plenty of exercises that can be got at a very little cost. Foremost are regular gymnastic exercises: by the regular practice of these all the muscles of the body are exerted in turn, and they have a great advantage in that a very short time is sufficient for them every day. Gymnastic exercises are not always or often performed in the open air, - that is one of their disadvantages, - but they are generally performed in well-ventilated rooms, which is the next best thing.

Another exercise which should be resorted to by a great many more than it is in the summer is swimming - an exercise by which almost all the muscles of the body are brought into play, and which is also beneficial from the point of view of cleanliness. And here I ought to say that youth is the time when habits of life are formed, and it is especially important that they should be formed in the right way; it is a time when such a habit as that of cleanliness, by which the action of the skin is promoted, should be formed, and when habits of attention to the action of the excretory organs of the body should be inculcated; because if the waste substances are not separated from the body as they are formed they will be re-absorbed into the blood, and will poison it; that poisoned blood will be distributed to the various tissues of the body, and I believe that we have no idea how many of the diseases of middle and old age ore due to the neglect of the proper action of the excretory organs.

After exercise there should be no fatigue felt for any length of time; if fatigue is felt for a long period after, it is a sign that either the exercise has been too violent or too prolonged; and that makes me remark that it is extremely important that exercise should not be taken too violently. It is necessary that there should be plenty, and, later on, much more violent and prolonged exercise can be taken with impunity than could have been taken during the period of growth.