Next, in order to cut this snarled and prostrate grain without missing any of it, the knife must have two motions: its forward motion, as drawn by the horses, and also a slashing sideways motion of its own. How was this to be done? McCormick's first thought was to cut the grain with a whirling wheel-knife, but this plan presented too many new difficulties. Suddenly the idea came to him--why not have a straight blade, with a back and forward motion of its own? This was the birth-idea of the _reciprocating blade_, which has been used to this day on all grain-cutting machines. It was not, like the divider, a wholly new conception; but Cyrus McCormick conceived it independently, and did more than any one else to establish it as the basic feature of the Reaper. The third problem was the supporting of the grain while it was being cut, so that the knife would not merely flatten it to the ground. McCormick solved this by placing a row of _fingers_ at the edge of the blade. These fingers projected a few inches, in such a way that the grain was caught and held in position to be cut. The shape of these fingers was afterwards much improved, to prevent wet grain from clogging the slit in which the knife slid back and forth. A fourth device was still needed to lift up and straighten the grain that had fallen. This was done by a simple revolving _reel_, such as fishermen use for the drying of their nets. Several of the abortive Reapers that had been tried elsewhere had possessed some sort of a reel; but McCormick made his much larger than any other, so that no grain was too low to escape it. The fifth factor in this assembling of a Reaper was the _platform_, to catch the cut grain as it fell; and from which the grain was to be raked off by a man who walked alongside of it. The sixth was the idea of putting the shafts on the outside, or stubble side, of the Reaper, making it a _side-draught_, instead of a "push" machine. And the seventh and final factor was the building of the whole Reaper upon one big _driving-wheel_, which carried the weight and operated the reel and cutting-blade. The grain-side end of the blade was at first supported by a wooden runner, and later--the following year--by a small wheel. [Illustration: FIRST PRACTICAL REAPING MACHINE Built and used by Cyrus Hall McCormick on Walnut Grove Farm, Va., in 1831]