It is important to correct, if possible, the misunderstanding which very naturally exists as to what physiologists and doctors mean by “experiment.” In ordinary language an “experiment” suggests a haphazard venture, the doing of something blindly and in ignorance, just “to see what will happen.” It is true that long ago in the eighteenth century there were men callous enough and ignorant enough to make such “fool’s experiments” on living animals. But when scientific men speak of “the experimental method” and the acquisition of knowledge by experiment, they do not allude to haphazard attempts to see what will happen when something extraordinary is done. The experiment of the experimental method is arranged so as to provide a definite answer to a definite question, and the question has been thought out by a man who knows the whole record of previous experiment and knowledge in regard to the subject which is under investigation. Thus in the inquiry as to the possible prevention of the deadly effect of snake poison introduced into the human body by the bite of snakes, the first question asked was, “Is it true, as sometimes stated, that a poisonous snake is not poisoned by having its own poison injected into its flesh?” The experiment was tried. The answer was, “It is true.” Next it was asked, “Is this due to the action of very small doses of the poison which pass constantly from the poison gland into the snake’s blood, and so render the snake ‘immune,’ as happens in the case of other poisons?” The experiment was tried. Snakes without poison glands were found to be killed by the introduction of snake’s poison in a full dose into their blood. Then it was found that a horse could be injected with a dose of snake poison, or half the quantity necessary to cause death, and that it recovered in a few days. The question was now put, “Is the horse so treated rendered immune to snake poison, as the snake is which receives small doses of poison into its blood from its own poison gland?” Accordingly the experiment was made. The horse was given a full dose of snake poison, and did not suffer any inconvenience. At intervals of two days it was given increasing injections of snake poison without suffering in any way, until at last an injection in one dose of thirty times the deadly quantity of snake poison--that is, enough to kill thirty unprepared horses--was made into the same horse, and it did not show the smallest inconvenience. The question was thus answered: Immunity to snake-bite can be conferred by the absorption of small quantities (non-lethal doses) of snake poison. The next question was this: “If something has been formed in the horse’s blood by this process, which is an antidote to snake poison, should it not be possible, by removing some of the horse’s blood and injecting a small quantity of it into a smaller animal, to protect that animal from snake bite?” The experiment was accordingly made.