FATIGUE. 311 



tribute its share to the total activities of the organism. 

 Yet these anatomical variations have their physio- 

 logical counterparts in every direction. A man con- 

 demned by his profession to sedentary habits may find 

 a splendid muscular system acting upon him as a 

 veritable parasite, or conversely a bulky nervous system, 

 coupled with too small a heart, may lead to an entire 

 mental existence on half rations. In some small 

 measure these maladjustments can be controlled, and 

 by such control the effective activity increased. 



In the study of fatigue it is the changes in the 

 material stored in the active cells at any one time that 

 claim attention. Normally exertion precedes fatigue. 

 When the muscles are exercised with the purpose of 

 increasing their strength, or the accuracy of their co- 

 ordination, their reactions do not improve with regu- 

 larity, or for an indefinite period. For the first two 

 days or so of systematic exercise the reactions may be 

 fairly satisfactory ; then follows a period of poor perfor- 

 mance which, after due time, gives way to improvement 

 that comes in waves. This indicates that the first 

 general result of exercising the body-cells, and specially 

 those of the central system, is not an immediate increase 

 in their powers of metabolism, but that this power is 

 only slowly improved. 



Even when cut off from their normal surroundings, 

 as when a muscle or part of the spinal cord is isolated, 

 the cells are for a time capable of doing work, but 

 under such circumstances soon become exhausted. If 

 the decrease in power under such circumstances is 

 measured, it is found that it steadily diminishes with 

 each discharge. When a muscle tested in this way has 

 been brought to the point at which it will no longer 

 respond, washing it out by passing a normal salt solu- 

 tion through the vessels will cause a return of power. 



