31. How does the velocity of a nervous process compare with other velocities in nature? 32. What is the general function of the nervous system? 33. Can you draw a diagram illustrating the architecture of a simple and of a more complex nervous system? 34. How can simpler nervous functions enter into a combination without completely losing their individuality? 35. What is meant by subcortical? 36. What is meant by afferent and efferent neurons? 37. How large is the surface of the brain? 38. What is meant by sensory and motor areas of the cortex? 39. Where is the seat of the soul? § 3. EXPLANATION OF THE FUNCTIONAL RELATION BETWEEN BRAIN AND MIND How the functional relation between the mind and the nervous system should be explained, is a question discussed for centuries and variously answered. But all the answers are essentially either the one or the other of these two: (1) Either the brain is a tool of the mind, or (2) it is an objectified conception of the mind itself. 1. _The Brain a Tool of the Mind_ Popular thought, supported by desires common to all human beings, readily accepts the view that mind is essentially different from matter, that its laws are in every respect different from the laws of material nature, and that the brain, being a part of the material nature, is simply the special tool used by the mind in its intercourse with nature. Consider what a contrast seems to exist between logical certainty and the mere probability derived from more or less deceptive sense impressions, between voluntary attention and sensual desire, between religious inspiration and ordinary perception, artistic creation and everyday work. Nevertheless, these highest as well as the lowest activities of the mind need a tool with which they can get into communication with the world; and this tool, says popular thought, is the brain. By means of this tool the mind can take possession of the world and shape it at will. This explanation of the functional relation between the mind and the nervous system agrees well with the facts above discussed concerning brain weight and intelligence, and nervous pathology and mental abnormality. That the magnitude, the architecture, the normal condition of a tool have an influence on the task performed, is plain enough. Many a piece of music can be played on a large organ having a great variety of stops, whereas its performance on a small instrument would be impossible. Raffael might have deserved the name of a great painter if born without arms, but the world would never have known it.