Ateil 2, 1909] 



SCIENCE 



525 



of the organism, and the fact that if it 

 succumbs all will be confusion and the 

 curtain must be rung down, the resistance 

 of the central nervous system to fatigue 

 would seem to be, like the known resistance 

 of the nerve fiber, an essential fact of the 

 animal economy. Yet nervous fatigue is 

 an undoubted fact and is manifested by 

 easily recognized physical and psychical 

 phenomena. Fatigue from overwork is one 

 of the common causes of neurasthenia. 



The behavior of the heart in a fatiguing 

 physical effort is always a matter of great 

 interest. When an individual is called 

 upon to perform intense and especially 

 prolonged work, the heart is largely the 

 key to the situation. There is no question 

 but that the work of the heart is then enor- 

 mously increased, partly because of the 

 heightened arterial pressure, and partly 

 because of the greater demands of the tis- 

 sues for oxygen. McCurdy found that 

 during a combination of the back and leg 

 lift used in the physical examination of 

 coUege students, the blood pressure, as 

 measured in the upper arm by the sphyg- 

 momanometer, rose more than sixty per 

 cent. After long-continued efforts, such 

 as in the Marathon runs, the heart is always 

 dilated, and often there are murmurs, in- 

 dicative of valvular insufficiencies. It is 

 not clear whether cardiac dilatation results 

 solely from the excessive arterial and intra- 

 ventricular pressure, or whether this ixa- 

 doubted cause is not reinforced by diminu- 

 tion of the tonus of the heart muscle due to 

 the action of the fatigue substances. In- 

 deed, the direct action of fatigue substances 

 on heart and arteries is much in need of 

 study. A sudden and acute dilatation may 

 be a very serious matter, either endanger- 

 ing the life of the individual at the time 

 or leaving permanent pathological effects. 

 In a well-trained heart, however, there 

 ought to be hypertrophy, as there is in a 

 well-trained voluntary muscle, and it does 



not appear that dilatation and hypertrophy 

 are necessarily deleterious results of severe 

 physical effort. 



Besides cardiac dilatation, severe effort 

 may produce other mechanical effects, such 

 as hernias, the rupture of muscles and of 

 blood vessels, and even the fracture of 

 bones, but these must be looked upon as 

 adventitious phenomena, possible but not 

 probable sequelae of excessive effort. 



Both albumin and easts are very fre- 

 quently found in the urine after excessive 

 physical effort, usually so with Marathon 

 runners. Why this occurs is not clear, but 

 from the apparent causative connection of 

 the toxins of infectious diseases with al- 

 buminuria, it may be questioned whether 

 the albuminuria of fatigue may not be due 

 to the action of fatigue substances on the 

 renal cells. In this connection a recent 

 discovery by Pearce and Sawyer is inter- 

 esting. They found that the serum of dogs 

 suffering from artificially produced nephri- 

 tis, when injected into normal dogs, caused 

 protein to appear in the urine. This dis- 

 covery suggests the question whether there 

 is a fatigue toxin which acts upon the 

 kidneys as a nephrotoxin. 



Excessive effort frequently brings on a 

 high temperature, which may last for days 

 afterward. It seems probable that this 

 fatigue fever, like the fevers caused by 

 bacterial toxins, is due to the action of 

 toxic fatigue substances, but here again 

 accurate study is wanting. 



The metabolic changes in the body in- 

 volved in fatiguing effort are much in need 

 of investigation by modern methods. Our 

 present knowledge of these changes need 

 not here be discussed. 



Fatiguing effort may thus result in a 

 large variety of phenomena. Some of these 

 have purely mechanical causes, but the 

 majority of them may probably be traced 

 primarily to the action, on the tissues, of 

 the specific fatigue factors. The phenom- 



