166 HUMAN PHYSIOLOGY 



How extensive and potent is this discharge has only 

 recently come to be appreciated. When a man shows 

 anger we can recognize by the tension of his muscles 

 that they are under stimulation. If he is pale we may 

 conclude that his circulatory system is involved in the 

 reaction. His fast heart would confirm this opinion. 

 We may state here what will be more fully described 

 at another time; that the alimentary canal and the 

 glands are also played upon by the impulses that issue 

 in moments of excitement. 



In the light of the facts emotion is seen to be a very 

 real form of exercise. As exercise may be wholesome 

 or unwholesome, reasonable or excessive, so emotion 

 may count for health or dispose to disease. People 

 who do not have many emotional stirrings are, in a 

 sense, untrained and may be wanting in endurance. 

 On the other hand, intense and frequent emotion is 

 a source of nervous fatigue. This must now engage our 

 attention for a little. 



Nervous Fatigue. We have said something about the 

 fatigue of the neuromuscular mechanism. It will be 

 recalled that the motor end-plates and the muscle 

 fibers themselves are subject to temporary loss of 

 capacity through use. The nerve cells may also be 

 vulnerable; the white matter is highly resistant. The 

 synapses through which effects are transmitted from 

 one unit to another are quite susceptible to fatigue. 

 When we have to do with the intricate organization of 

 the brain we cannot so easily analyze what we call a 

 state of fatigue. Fatigue that is severe and sharply 

 localized probably means in every case a loss of power 

 to act, but diffuse fatigue in the central nervous 

 system has another characteristic; it resembles an 

 intoxication in which there is much unprofitable activity. 



Perhaps we may recognize two types of nervous fatigue. 

 There is the daily weariness which leads to sleep and is 

 neutralized in the course of the night's rest. The 

 other sort is more insidious and has the perverse symp- 



