In animal organs and human tools we have the main difference between men and animals. The animal obtains its food and subdues its enemies with its own bodily organs; man does the same thing with the aid of tools. Organ (organon) is a Greek word which also means tools. Organs are natural, adnated (grown-on) tools of the animal. Tools are the artificial organs of men. Better still, what the organ is to the animal, the hand and tool is to man. The hands and tools perform the functions that the animal must perform with its own organs. Owing to the construction of the hand to hold various tools, it becomes a general organ adapted to all kinds of work; it becomes therefore an organ that can perform a variety of functions. With the division of these functions, a broad field of development is opened for men which animals do not know. Because the human hand can use various tools, it can combine the functions of all possible organs possessed by animals. Every animal is built and adapted to a certain definite surrounding. Man, with his tools, is adapted to all circumstances and equipped for all surroundings. The horse is built for the prairie, and the monkey is built for the forest. In the forest, the horse would be just as helpless as the monkey would be if brought to the prairie. Man, on the other hand, uses the axe in the forest, and the spade on the prairie. With his tools, man can force his way in all parts of the world and establish himself all over. While almost all animals can live in particular regions, such as supply their wants, and if taken to different regions cannot exist, man has conquered the whole world. Every animal has, as a zoölogist expressed it once, its strength by which means it maintains itself in the struggle for existence, and its weakness, owing to which it falls a prey to others and cannot multiply itself. In this sense, man has only strength and no weakness. Owing to his having tools, man is the equal of all animals. As these tools do not remain stationary, but continually improve, man grows above every animal. His tools make him master of all creation, the king of the earth.