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SCIENCE 



[N. S. Vol. XXIX. No. 744 



the term exhaustion there are evidences of 

 the profound action of toxic substances. 



Ever since Eukles, the progenitor of 

 Hayes, Dorando and Longboat, ran and 

 won the first Marathon race and gave his 

 life for the privilege of announcing to the 

 Athenians the victory of Miltiades, the 

 phenomena of fatigue have been of pro- 

 found interest. The cause of the death of 

 Eukles can only be conjectured, but the 

 laboratories, the gymnasia and the race 

 tracks of modern days have given us many 

 data of value. Without attempting to re- 

 view completely the chemical, physical and 

 psychical phenomena of fatigue, let us con- 

 sider some of the most common and most 

 striking of these. The universal character- 

 istic of fatigued muscle is that its lifting 

 power for a given stimulus is diminished. 

 In the voluntary muscles of cold-blooded 

 animals the process of relaxation is always 

 slowed, often enormously, but this does not 

 seem to occur with warm-blooded muscles. 

 There seems no doubt that the muscles can 

 endure, without detriment, great abuse 

 from both of the factors engaged in the 

 causation of fatigue. Any one who has 

 observed the activity of an isolated and 

 electrically stimulated muscle, from which 

 the blood stream has been cut off and from 

 which the accumulated fatigue substances 

 are occasionally washed by a stream of oxy- 

 genated physiological salt solution, can not 

 fail to be impressed by the long continu- 

 ance of the muscle's activity and the enor- 

 mous resistance to exhaustion which it 

 shows, even when no food enters it. The 

 muscle possesses within its cells material 

 for performing an incredible amount of 

 work. And no less resistance is shown by 

 the trained muscle to the action of fatigue 

 substances. Thurston estimates the aver- 

 age amount of a man's work per day as 

 two million foot pounds. Carpenter cal- 

 culated that in the last of the old-style six- 

 day bicycle races, held in New York in 



1898, the winner. Miller, performed on the 

 first day more than fifteen million foot 

 pounds of work, and on each of the six days 

 an average of more than nine and one half 

 million foot pounds, the latter being nearly 

 five times man's daily average. Notwith- 

 standing this great effort. Miller com- 

 peted during the following month in a 

 twenty-four hour race, and two months 

 thereafter he won a second six-day race, 

 breaking his previous record. 



The results of fatiguing muscular effort 

 are not confined to the muscles. The 

 proper conditions for fatigue are, at the 

 same time, presented to the nervous system, 

 partly because of its own efforts and partly 

 through the fatigue substances of muscular 

 origin circulating in the blood. It is un- 

 fortunate that we know so little regarding 

 the capability of fatigue of the nervous 

 system. The one certain fact is that the 

 nerve fiber can be fatigued only with diffi- 

 culty. The former and still common idea 

 that the brain and spinal cord are readily 

 fatiguable and, in fact, are the first part of 

 the individual to succumb in a contest, 

 seems not to be justified by the experi- 

 mental work of Hough, Storey, "Wood- 

 worth, Joteyko, Kraepelin and others. In 

 attempting last year to discover an efficient 

 method of fatiguing the spinal cord by arti- 

 ficial stimulation, I could find no conclusive 

 evidence that genuine fatigue had been ac- 

 complished. Sensations of fatigue are a 

 resultant, chiefly, of the fatigue of tissues 

 situated outside the brain and spinal cord. 

 It seems not unreasonable, therefore, to 

 believe that the central nervous system is 

 highly resistant to fatigue. It is a note- 

 worthy fact that it is the last part of the 

 body to lose in weight in starvation— all 

 the other tissues contribute of their sub- 

 stance that it may be preserved. In cer- 

 tain diseases, too, it is the last tissue to be 

 attacked. When one considers the indis- 

 pensable role which it plays in the drama 



