This idea can be very well demonstrated by the method that present-day physicians have adopted, of inoculating a person with the same element which makes him ill. There is no better demonstration of this idea than the practice of inoculation. This puts a person in harmony with the thing that is opposed to his nature. If one understands this principle one can inoculate oneself with all that does not agree with one, and with that to which one is continually exposed and from which there is no means of getting away. Woodcutters do not as a rule get sunstroke: seamen do not catch cold easily. The reason is that the former have made themselves sunproof while the latter have made themselves waterproof.