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theory—this story that we are immune because of a kind of battle royal between our phagocytes and marauding microbes, this yarn had thrown the searchers of Europe into an uproar. The microbe hunters of Germany and Austria for the most part did not believe it—on the contrary, tempted to believe it by its simplicity and prettiness, they denied it with a peculiar violence. They denounced Metchnikoff in congresses and by experiments. One old German, Baumgarten, wrote a general denunciation of phagocytes, on principle, once a year, in an important scientific journal. For a little while Metchnikoff wavered; he nearly swooned, he couldn't sleep nights, he thought of going back to his soothing morphine; he even contemplated suicide once more—oh! why could not those nasty Germans see that he was right about phagocytes? Then he recovered. Something seemed to snap in his brain, he became courageous as a lion, he started a battle for his theory—it was a grotesque, partly scientific wrangle—but, in spite of all its silliness, it was an argument that laid the foundations of the little that is known to-day about why we are immune to microbes.

"I have demonstrated that the serum of rats kills anthrax germs—it is the blood of animals not their phagocytes. that makes them immune to microbes," shouted Emil Behring, and all the bitter enemies of Metchnikoff sang Aye in the chorus. The scientific papers published to show that blood is the one important thing would fill three university libraries.

"It is the phagocytes that eat up germs and so defend us," roared Metchnikoff in reply. And he published ingenious experiments which proved anthrax bacilli grow exuberantly in the blood of sheep which have been made immune by Pasteur's vaccine.

Neither side would budge from this extreme, prejudiced position. For twenty years both sides were so enraged they could not stop to think that perhaps both our blood and our phagocytes might work together to guard us from germs. That