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but he focussed up and down, and fussed, and looked at a dozen thin bits of glass with blood between them. Presently these spaces began to turn into queer pear-shaped living creatures for him. In the blood of every beast dead of Texas fever he found them—always inside the corpuscles, wrecking the corpuscles, turning the blood to water. Never did he find them in the blood of a healthy northern cow. . . . "It may be the microbe of Texas fever," he whispered, but like a good peasant he did not jump to conclusions—he must look at the blood of a hundred cows, sick and healthy, he must examine millions of red blood cells to be sure. . . .

By now the hottest weather had passed, it was September, and in Field No. 2, the northern cattle, all four of them, kept on grazing and grew fat—there were no ticks there. And Smith muttered: "We'll see if it's the ticks who are to blame!" and he took two of these unharmed northern beasts and led them into Field No. 1, where so many beasts had died—in a week a few of the little red-brown bugs were crawling up these new cow's legs. In a little more than two weeks one of these cows was dead, and the other sick, of Texas fever.

But there never was a man who needed more experiences to convince him of something he wanted to believe. He must be sure! And there was still another simple trick he could try—call it an experiment if you wish. From North Carolina, from the fatal fields down there, came large cans and these cans were filled with grass, that swarmed with ticks, crawling, thirsty for the blood of cows. These cans Theobald Smith took on to Field No. 3, where no southern cattle or their blood-sucking parasites had ever been, and he plodded up and down this field, and all over it he sowed his maybe fatal seed—of ticks. Then four northern cattle were led by Kilborne on to this field—and in a few weeks their blood ran thin, and one died, and two of the remaining three had severe bouts of Texas fever but recovered.