78 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 
tion. Education lowers the threshold of the sensory neurones 
and of the association areas. The formation of habits, also, 
depends upon this law—as the result of its influence, such com- 
plex actions as walking, writing, speaking, etc., are performed 
altogether by the lower centers and apparently without the 
least intervention of consciousness. 
Variations of individual temperament depend largely upon 
variations of the neurone threshold in different neurone sys- 
tems in different individuals. If the threshold value of the 
motor neurones is low, we find a careless or impulsive person, 
if the neurones of the emotional centers be the more unstable, 
an excitable person. If the neurones have a low threshold to 
nerve impulses and a high threshold to external changes, the 
owner is highly imaginative, he sees visions and dreams dreams. 
If the opposite relationship is found, he is observant and matter- 
of fact. The value of the neurone threshold is one of the im- 
portant factors in the production of individual peculiarities. 
Other factors, such as the development of association paths, 
education, hereditary and environment are closely associated 
with this and with other phases of neurone metabolism. 
Abnormally, the neurene threshold may vary within very 
wide limits. In melancholia the thresheld may be tremendously 
increased. In delusional insanity the threshold value of certain 
neurone systems is lowered. In these cases the reaction time is 
greatly increased. 
In neurasthenia the threshold value is increased, in hysteria 
it is decreased. In neurasthenia the increase of the threshold 
value is probably due to a decrease in the cell’s power of re- 
cuperation, a nutritional disease. In hysteria the molecules of 
certain neurone systems are unstable to an abnormal degree. 
This too, is an instance of faulty metabolism. Rarely is the 
neurone at fault in such cases. Usually the neurones are 
starved, poisoned or overworked. 
All our relations with the external world depend upon varia- 
tions in the metabolic processes of the neurone. Our percep- 
tions are true, our decisions wise and our deeds rational just to 
the degree in which the neurone metabolism is normai. A de- 
ficiency or an excess of any of the internal secretions; a lack 
of food, whether due to imperfect diet or to imperfect digestion 
and assimilation; intoxications, whether due to the ingestion 
of poisons or to the retention of excretory compounds; lack of 
oxygen, poor circulation, the lack of normal stimuli or the re- 
ception of excessive stimulation; all these tend to render our 
perceptions fautly, our judgments imperfect and our actions 
unjust. 
