But he tried it. He took a good fat yearling heifer, put her in a box-stall, and day after day put hundreds of clean baby ticks on her, holding her while these varmints crawled away beneath her hair to get a good grip on her hide. Then day after day, while the ticks made their meals, he cut little gashes in her skin to get a drop of blood to see if she was becoming anemic. And one morning Theobald Smith came into her stall--for the usual routine--he put his hand on that heifer.... What was this? She felt hot! Very hot! Suspiciously too hot! She drooped her head, and would not eat--and her blood which before had welled out from the gashes thick and rich and red--that blood ran very thin and darkish. He hurried back to his attic with samples of the blood between little pieces of glass.... Under the microscope it went, and sure enough!--here were twisted, jagged, wrecked blood corpuscles instead of good even round ones with edges smooth as a worn dime. And inside these broken cells--it was fantastical, this business!--were the little pear-shaped microbes.... Here was the fact, stranger than any pipe-dream--for these microbes must have come up from North Carolina on old ticks, had gone out of the old ticks into the eggs they had laid in the glass dishes, they had survived in the baby ticks hatched out these eggs--and these babies had at last shot them back, ready to kill, into their destined but completely accidental victim, that yearling heifer! In a flash all those mysterious questions cleared up for Theobald Smith. It was not the old, blood-stuffed tick but its child, the baby tick, who sneaked the assassin into the northern cows; it was this little five- or ten-day-old bug who carried the murderer. Now he saw why it was that fields took so long to become dangerous--the mother ticks have to drop off the southern cattle; it takes them some days to lay their eggs; these eggs take twenty days or more to hatch; the tick babies have to scamper about to find a cow’s leg to crawl up on--all that takes many days, weeks. Never was there a simpler answer to a problem which, without this strange chance, might not yet be solved.... So soon as he could hatch out other thousands of ticks in warm glass dishes, Theobald Smith proceeded to confirm his marvelous discovery; he proved it clean. For every northern cow, on whom he stuck his regiments of incubator ticks, came down with Texas fever. But he was a glutton for proofs, as you have seen, and when the summer of 1890 waned and it grew cold, he installed a coal-stove in a stable, hatched the ticks in a heated place, put a cow in the hot stable, stuck the little ticks diligently onto the hide of the cow, the stove instead of the sun made them grow as they should--and the cow got Texas fever in the winter, a thing which never happens in nature!