All mental process accompanied by neural process--Gradations in nervous response from lower organisms to man--Behavior of many animals often an automatic adjustment to simple external agents-- Tropisms--Certain apparently complex volitions probably only tropisms--Complicating factors--Many tropic responses apparently purposeful--Tropisms grade into reflex actions and instincts-- Adjustability of instincts opens the way for intelligent behavior--Modification of habits possible in lower animals--Some lower vertebrates profit by experience--Rational behavior-- Conceptual thought probably an outgrowth of simpler psychic states--The capacity for alternative action in higher animals--The elemental units of the nervous system are the same in lower and higher animals--Neuron theory--Establishment of pathways through the nervous system--Characteristic arrangements of nerve cells subject to inheritance--Different parts of the cortex yield different reactions--Skill acquired in one branch of learning probably not transferred to another branch--Preponderance of cortex in highest animals--Special fiber tracts in the spinal cord of man and higher apes--Great complexity in associations and more neurons in the brain of man--The nervous system in the main already staged at the time of birth--Many pathways of conduction not yet established--The extent of the modifiable zone unknown-- Various possibilities of reaction in the child--Probable origin of altruistic human conduct--Training in motive necessary--Actual practise in carrying out projects important--Interest and difficulty both essential--The realization of certain possibilities of the germ rather than others is subject to control--We must afford the opportunity and provide the proper stimuli for the development of good traits--Moral responsibility. VIII MENTAL AND NERVOUS DEFECTS 228