THE NEUROMUSCULAR SYSTEM: FATIGUE 109 



and by means of synapses which have not been fatigued. 

 The new application would be vain if there were not still 

 muscular resources available and possibilities of synaptic 

 transmission from the projection fibers of the cerebrum to 

 the motor neurons of the cord (Fig. 20). 



What shall we say of the soldier who is roused from 

 what seemed to be utter fatigue by the close pursuit of 

 the enemy and the whistle of bullets? Is this a simple 

 case of setting up brain currents which arrive at the 

 motor centers by fresh routes and unimpaired synapses? 

 It may be so in part, but whenever a strong emotional 

 reaction is entailed there are likely to be chemical rein- 

 forcements of muscular capability. This is a matter which 

 may well be left for discussion in another connection. 

 The general principle has been stated in the last chapter 

 (see page 92), where the augmented production of adren- 

 alin in times of excitement was mentioned. 



The remarkable postponement of fatigue in the case 

 of those who like to dance is worthy of some comment. 

 Consider the country girl, whose daily tasks are heavy 

 enough to leave her quite tired at nightfall and ready for 

 an early bedtime. On the exceptional evening when there 

 is to be a party the usual day's work may have been faith- 

 fully done, but there may be no signs of the accustomed 

 weariness. Instead, she goes to the dance and for hours 

 pursues a form of vigorous exercise in which the muscles 

 used are, in the main, the same which were called upon 

 in the domestic round. Perhaps the emotional state is 

 intense enough to warrant the belief that internal secre- 

 tions are modified to support the muscular activity. 

 Whether this is so or not, we can see that the conditions 

 favor an extensive and symmetric stimulation of the 

 cortical areas. 



When the girl in question was engaged in sweeping a 

 room she was held to her dull duty by certain internal 

 stimuli of an obscure but evidently monotonous char- 

 acter. The "sense of duty" as realized in consciousness is 

 attended by the transmission of impulses to the motor 



