[Illustration: Diagram to show the parts of the brain and action of the different parts of the brain.] Functions of the Cerebrum.--In general, the functions of the different parts of the brain in man agree with those functions we have already observed in the frog. The cerebrum has to do with conscious activity; that is, thought. It presides over what we call our thoughts, our will, and our sensations. A large part of the area of the outer layer of the cerebrum seems to be given over to some one of the different functions of speech, hearing, sight, touch, movements of bodily parts. The movement of the smallest part of the body appears to have its definite localized center in the cerebrum. Experiments have been performed on monkeys, and these, together with observations made on persons who had lost the power of movement of certain parts of the body, and who, after death, were found to have had diseases localized in certain parts of the cerebrum, have given to us our knowledge on this subject. [Illustration: Diagram of the nerve path of a simple reflex action.] Reflex Actions; their Meaning.--If through disease or for other reasons the cerebrum does not function, no will power is exerted, nor are intelligent acts performed. All acts performed in such a state are known as _reflex actions_. The involuntary brushing of a fly from the face, or the attempt to move away from the source of annoyance when tickled with a feather, are examples of reflexes. In a reflex act, a person does not think before acting. The nervous impulse comes from the outside to cells that are not in the cerebrum. The message is short-circuited back to the surface by motor nerves, without ever having reached the thinking centers. The nerve cells which take charge of such acts are located in the cerebellum or spinal cord. Automatic Acts.--Some acts, however, are learned by conscious thought, as writing, walking, running, or swimming. Later in life, however, these activities become automatic. The actual performance of the action is then taken up by the cerebellum, medulla, and spinal ganglia. Thus the thinking portion of the brain is relieved of part of its work. Bundles of Habits.--It is surprising how little real thinking we do during a day, for most of our acts are habitual. Habit takes care of our dressing, our bathing, our care of the body organs, our methods of eating; even our movements in walking and the kind of hand we write are matters of habit forming. We are bundles of habits, be they good ones or bad ones.