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 virulence or has been got rid of by the ordinary methods of defence. In either case the microbe is beaten. Life or death then depends only on the answer to the question whether its progress had or had not done fatal damage before the turn of the tide arrived.

The long and patient study of these subjects by experimental methods to which I have referred has enabled us to come to the aid of Nature along both these lines of defence in this war and brilliant successes have been obtained. Formerly the most feared of camp diseases was typhoid or enteric fever which cost us the lives of so many brave men in the Boer War, and in India was more fatal even than cholera. By inoculating all our troops before they went into the War with vaccine consisting of many millions of the microbes of typhoid fever we induced the same changes in the blood as actually take place in an attack of the fever itself. This could be done without danger of bringing on the disease because fortunately Nature does not distinguish 52