EXCRETION AND FATIGUE 209 



The presence of fatigue poisons has been shown repeatedly by 

 experiments similar to the above. For example, a dog has been 

 kept running until he is very much fatigued ; some of this dog's 

 blood is then introduced into the veins of a dog that has been 

 kept quiet the whole day. Immediately the resting dog shows all 

 the signs of being a tired dog. 



243. Fatigue may be general. We have all been taught 

 that "a change of work is the best kind of rest." To a 

 certain extent this is true. When I am reading a hard book 



to. 



ii in nun iim 



llilllllHllllllllllllllllllllllilllllllllllllMllill))li|Ullii|l 



FIG. 79. General fatigue as measured by the ergograph 



The ergograph records the frequency and the strength of a pull exerted by a finger, the 

 resf of the hand being held firmly in place. These two records were made by a medical 

 student on the same day : a, before beginning his day's work at college ; l>, at the end of 

 the day's work. The height of the vertical lines shows the difference in energy, or strength, 

 of each pull. The difference between the bases shows relative time of application 



and begin to doze over it, I am not too tired to play a game 

 of tennis or even to read an interesting novel. But beyond 

 a certain point fatigue affects the whole body; getting tired 

 from study unfits one for muscular work or play. This is shown 

 by certain kinds of experiments that were first carried out 

 in Italy. 



Records made on the ergograph by any person will show great 

 variations, according to the condition of the body. A record made 

 early in the morning will differ from one made at the end of the day ; 

 a record made after taking a nap in the afternoon will differ from 

 one made at the close of a game of chess (see Fig. 79). Although 



