And because of these close relations the great characteristic of living beings is the necessity and power of conformity to environment. Hence a very common definition of life is the continual adjustment of internal relations to external relations or conditions. To a very slight extent man can rise superior to certain of the ruder elements of his surroundings, but he gains this victory only by learning and following the laws of the very environment which he succeeds in subjecting to himself. Indeed his higher development and finer build bring him into touch with an indefinitely wider range of surroundings than even the lower animal. Forces, conditions, and relations which never enter the sphere of life of lower forms, crowd and press upon him and he cannot escape them. His higher position, instead of freeing him from dependence upon environment and subjection to law, makes him thus more sensitive, as well as more capable of exact conformity to an environment of almost infinite complexity; and more sure of absolute ruin, if ignorant, negligent, or disobedient. The words of the German poet are literally true: "Nach ehernen, eisernen, grossen Gesetzen, Müssen wir alle unseres Daseins Kreise vollenden." But man is an animal. And the principal characteristic of an animal is that it eats a certain amount of solid food. The plant lives on fluid nutriment, and this comes to it by the process of diffusion in every drop of water and breath of air. The acquisition of food requires no effort, and the plant makes none. It has therefore always remained stationary and almost insensible. Not taking the first step it has never taken any of the higher ones. But solid food would not, as a rule, come to the animal--though stationary and sessile animals are not uncommon in the water--he must go in search of it. This called into play the powers of locomotion and perception. And in the sequence of function we have seen digestion calling for the development of muscle; and muscle, of nerve and brain. And the brain became the organ of mind. Man as a mere animal is necessarily active and energetic; otherwise he stagnates and degenerates. Labor is a curse, but work a blessing; and man's best work, of every kind, is done in the friction of life, not in ease and quiet. Man is, further, a being composed of cells, tissues, and organs, which were successively developed for him by the lower animal kingdoms. The old view, that man was the microcosm, had in it a certain amount of every important truth. We need to be continually reminded of our indebtedness in a thousand ways to the lowest and most insignificant forms of life.