The invention of the bow-and-arrow was of tremendous importance in securing food. It is not known what led to its invention, although the discovery of the flexible power of the shrub, or the small sapling, must have occurred to man as he struggled through the brush. It is thought by some that the use of the bow fire-drill, which was for the purpose of striking fire by friction, might have displayed driving power when the drill wound up in the string of the bow flew from its confinement. However, this is conjectural; but, judging from the inventions of known tribes, it is evident that necessity has always been the moving power in invention. The bow-and-arrow was developed in certain centres and probably through trade and exchange extended to other tribes and groups until it was universally used. It is interesting to note how many thousands of years this must have been the chief weapon for destroying animals or crippling game at a distance. Even as late as the Norman conquest, the bow-and-arrow was the chief means of defense of the Anglo-Saxon yeoman, and for many previous centuries in the historic period had been the chief implement in warfare and in the chase. The use of the spear in fishing supplemented that of the hook, and is found among all low-cultured tribes of the present day. The American Indian will stand on a rock in the middle of a stream, silently, for an hour if necessary, watching for a chance to spear a salmon. These small devices were of tremendous importance in increasing the food supply, and the making of them became a permanent industry. Along with the bow and arrow were developed many kinds of spears, axes, and hammers, invented chiefly to be used in {88} war, but also used for economic reasons. In the preparation of animal food, in the tanning of skins, in the making of clothing, another set of stone implements was developed. So, likewise, in the grinding of seeds, the mortar and pestle were used, and the small hand-mill or grinder was devised. The sign of the mortar and pestle at the front of drug-stores brings to mind the fact that its first use was not for preparing medicines, but for grinding grains and seeds.