But we may ask, "If this is true, where do medicine and surgery come in? Why do they ever interfere if nature is so very wise?" Because nature overdoes the thing every now and then. Nature is first enormously wise and then a little blind. In another example I can bring this out a little better. You have sprained your knee and the knee gets very stiff. That in itself is good; it is a defencive reaction. The stiffness is like a splint. The knee ought to be kept quiet. So far so good. But nature overdoes the thing. The knee ought to be kept quiet, but for how long? We will say three days more or less, according to the severity of the injury. Then you have to fight nature which stiffens the knee too much. You have to fight it by the use of the knee, by walking or by massage, which is not, however, so good as walking. If we respect blindly what nature does in stiffening the knee even to the exclusion of nature's other functions, such as walking, then the knee will get worse. One of the greatest improvements in the modern treatment of sprains, is that we no longer keep the patient in bed and put plaster of Paris on, which makes the sprain last for months sometimes; but we let him walk at once on the sprained ankle, whereby the attempts of nature to cure by stiffening are not carried too far. Another example of how nature overdoes things is in the formation of scar tissue. If a scar did not form to close the wound, the wound would remain open. Hence the scar is vastly better than nothing. But scar tissue is never as good as the original tissue. One of its known ill results is contraction, so that a scar on the hand or on the neck often draws the part out of place. Then we have to fight nature. We have to go against the workings of nature by surgery, in order to get the person right.