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North Carolina, and mixed them with hay, and fed them to a susceptible northern cow kept carefully in a special stable. But nothing happened; the cow seemed to relish her new food, she got fat. He tried drenching another cow with mashed up ticks made into a soup—but that cow too seemed to enjoy her strange dose. She prospered on it.

It was no go—cows didn't, apparently, get the microbe by eating ticks; he was mixed up for a while. And other plaguey questions kept him awake nights. Why was it that it took thirty days or more, after the southern tick-loaded cows came on the field, for such a field to become dangerous? Stockmen knew this too; they knew they could mix just-arrived southern cows with northern ones, and keep them together twenty days or so, and then if they took the northern ones away—they would never get Texas fever; but if you left them in that field a little longer (even if the southern cows were taken away) bang! would come the fatal epidemic into the herd of northerners. That was a poser!

Then one day in this summer of 1890, by the most strange, the most completely unforeseen of accidents, every jagged piece of the puzzle fell into its proper place. The solution of the riddle fairly clubbed Theobald Smith; it yelled at him; it forced itself on him while he was busy doing other things. He was at all kinds of experiments just then; he was bleeding northern cows for gallons of blood to give them an anemia—to make sure those funny little pear-shaped objects he had found in the corpuscles of Texas fever cattle were microbes, and not simply little changes in blood that might come from anemia. He was learning to hatch nice clean young ticks artificially in glass dishes in his laboratory; he was still laboriously picking ticks off southern cows—and sometimes he failed to get them all off and the experiments went wrong—to prove that tickless southern cows are harmless to northern ones; he was discovering the strange fact that northern calves get only a mild fever on a field fatal to their mothers. He fussed about