II. Not only are the brain-cells developed by exercise, but it also appears to be a fact that the mind appears actually to be _nourished_ by knowledge of the outside world of things. The raw material of thought is taken into the mind and there is digested by the thought-processes, and is afterward actually _assimilated_ by the mind in a manner strikingly similar to the processes of the physical organs of nutrition. A mind to be at its best must be supplied with a normal amount of mental nourishment. Lacking this, it tends to become weak and inefficient. And, likewise, if its owner is a mental glutton and furnishes too much nourishment, particularly of a rich kind, there is a tendency toward "mental dyspepsia" and indigestion--the mind, unable to assimilate the mental food furnished it, is inclined to rebel. Moreover, if the mind be supplied with mental food of only one kind--if the mind is confined to one narrow field of thought--it weakens and the mental processes become impaired. In many ways is this curious analogy apparent. Not only does the mind need development, but it also needs intelligent cultivation. For it may be _developed_ by improper objects of thought just as well as by the proper ones. A rich field will grow tares and weeds as well as good grain or fruit. Thought-culture should not be confined to the _development of a strong and active mind_, but should be also extended to the _cultivation of a wise and intelligent mind_. Strength and Wisdom should be combined. Moreover there should be sought a harmonious and normal development. A one-sided, mental development is apt to produce a "crank," while a development in unhealthy mental fields will produce an abnormal thinker tending dangerously near to the line of insanity. Some "one-idea" men have great mental power and development, but are nevertheless unbalanced and impractical. And insane persons often have strongly developed minds--developed abnormally.