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 finding every single effect a tick might have on a northern cow--it might do other damages besides giving her Texas fever...? Then came that happy accident. He asked himself: “If I should put good clean young ticks, hatched in glass dishes in my attic, ticks who never have been on cattle or on a dangerous field--if I should put such ticks on a northern cow and let them suck their fill of her blood--could those ticks take out enough blood to give the cow an anemia?” It seems to me to have been an aimless question. His thoughts were a thousand miles away from Texas fever....