654 POPULAR SCIENCE MONTHLY. 



Dr. Stanley Hall has said somewhere that the time may not he 

 far away when we can say that what is physiologically right is 

 morally right that is, whatever begets the best physiological 

 conditions will produce the best moral character. 



II. 



If brain fatigue interferes with the readiness and accuracy of 

 one's intellectual operations and estranges the emotional nature, 

 it is important to know what are the agencies most commonly 

 found in home and school which produce this condition ; for when 

 the various qualities of which dullness and irritability are types 

 are characteristic of one's childhood they tend to become per- 

 manent, thus determining one's character. It is shown by neu- 

 rology that any mental act oft repeated leads to the establish- 

 ment of correlated neural processes which make the reproduction 

 of that act continuously easier until it becomes automatic, when 

 all the causes which originally produced it even if with conscious 

 effort on the part of the individual will in time awaken it with- 

 out any such difficulty. If now it be remembered that brain 

 fatigue is due to some degree of exhaustion of cerebral cells, it 

 will be apparent that one of the most important sources of fa- 

 tigue is inadequate nutrition of the brain. Nerve cells, like all 

 other cells in the body, repair themselves by absorbing from the 

 blood those materials suited to their particular needs. If the 

 blood does not carry to them a sufficient quantity of the right 

 elements of food to meet the demands made upon them, then 

 while thus neglected they will be in a partially exhausted state 

 from sheer inability to obtain nutriment. Just so a field of 

 wheat in poor soil will bring forth imperfect grain, or a fruit 

 tree unable to find the proper elements of nutrition will bear 

 defective apples or pears or peaches. 



All life of whatsoever kind requires a proper sort and adequate 

 amount of nutrition in order that it may develop in a vigorous, 

 healthy manner. Experiments have been conducted in rearing 

 tadpoles and pond snails in various sized vessels of water, where 

 the opportunities for nutrition corresponded with the quantities 

 of water inclosed, and it has been found that the less the amount 

 of water the smaller the animal. Animals reared in this way 

 may be arranged in a series increasing in size according to the 

 quantity of water in which they have been placed.* Many mam- 

 mals and birds are found to have their centers of distribution in 

 the northern regions, and they diminish in size from the northern 

 to the southern latitudes, thus indicating that the ability to ob- 

 tain food determines the degree of development of the bird \ or 



* Donaldson, op. ciL, p. 139. { Ibid., p. 59. 



