Mil. \KK\mS S1STK.M AND ITS ( '< >\SKK\ A I'll i \ 



potassium phosphate. These arc all acidic in nature, and 

 it is supposed thai any other acid, introduced experi- 

 mentally, will have a similar effect, rndelined fatigue 

 substances probably exist in addition to the ones named 

 and they may not all have an acid character. A most 

 important fact to be noted with regard to these metabolic 

 products is this: the same compounds which in high con- 

 centration can poison the muscle to the point of apparent 

 paralysis, act as stimulants when they are present in small 

 amounts. In this we find one explanation of the favorable 

 effect of moderate preliminary exercise upon muscular 

 capacity. A muscle is not so efficient when it is first 

 aroused to activity after a period of rest as it is when it 

 has been used for a time. 1 



The phenomenon referred to the gain in power which 

 comes with a brief series of contractions is spoken of as 

 I lie "stair-case effect," or often, using a ( lerman equivalent, 

 as the Treppe. The proof that it is due in part at least !. 

 the so-called fatigue substances we owe to Lee of Colum- 

 bia. Other factors undoubtedly enter in; when one is 

 "warming up" one profits by the adaptation of the cir- 

 culatory system to the new requirements and, perhaps, 

 also by changes in the activity of the organs of internal 

 secretion. But when all allowance has been made for 

 such sources of reinforcement, we must still attribute 

 much to the favorable influence of the products of activ- 

 ity exerted before their accumulation has become excessive. 



We are now in position to consider the probable seat of 

 fatigue in the iieuromuscular apparatus. Recalling the 

 unit of this mechanism as previously defined, we find 

 that the possibilities are more numerous than would at 

 first be supposed. The muscle-fiber may be fatigued. 

 The junction of nerve and muscle, the motor end-plate 1 , 

 is anol her structure which is subject to impairment by 

 its own use. This is, indeed, a relatively weak link in 

 t he chain. Fatigue of the nerve-fiber may be disregarded; 

 the enduring nature of the white matter has already been 

 1 !". S. LIT, 1'np. Sri. Monthly, February, HMO. 



