It is surprising, in these days when everybody is an authority on matters of health, how few people there are who can tell you what it really is. The majority, if asked to describe it, would probably say that a man is healthy when he is not ill. [Sidenote: Health, not illness, the standard.] Now when you come to analyse this statement, it conclusively shows one thing, namely that people take illness as the standard. Most human beings, in civilised countries at any rate, have something the matter with them--a weak digestion, tendency to sore throats or colds, or a predisposition to ailments of one sort or another. Yet the fact that most people suffer from illness is no reason for calling it a natural condition. It is health that is natural; illness is an anomaly. Medical men themselves are the first to recognise the truth of this statement. Animals as a rule are sound and vigorous so long as they are in a wild state. It is only when they are in captivity that they become delicate. Similarly savages are much freer from disease than civilised races. It is when they live in artificial surroundings that they become prone to sickness. Health is not a negative thing. It is a state in which every part is sound and acts in harmony with every other part. [Sidenote: The nature of health.] A motor-car consists of a great number of different parts--the gear, the engine, the petrol supply, the firing. It is not sufficient that each section should be in good order. For each must also fit in, both mechanically and in point of time, with every other. The petrol pipe may be clear, but unless the spark reaches the cylinders exactly in the nick of time there will be misfiring, and a loss of power in consequence. This loss of power is not the only harm done. It means that there will be unnecessary friction also, causing extra wear and tear to the engine and gear. If this occurs but seldom, and is put right at once when detected, little damage may be done. If repeated often, and allowed to go on uncared for, the whole structure of the car will suffer and the life of the machine be shortened. It does not follow that the car will come to a standstill. It will continue to run, but badly. For like every other engine, it has the faculty of compensation. That is to say, when one part is out of order other parts will take on some of its work, and help, for a time at least, to make good the deficiency. For instance, in a four-cylinder car one of the cylinders may cease to act. Yet the other three will take on a certain part of the work, and help to some extent to make up the deficiencies of the faulty one.