ON MENTAL AND MUSCULAR FATIGUE. 293 



In addition, a further and separable effect of previous activity is that 

 initial increase in the height of contraction spoken of as Bowditch's 

 ' staircase.' It is a common opinion that this phenomenon is to be 

 observed in muscle in a fresh state. I have made certain of the faci 

 that it is capable of demonstration, not near the final stage of fatigue, 

 but at a surprisingly late stage of fatigue. Thus it is possible by the 

 interpolation of a short period of rest and a subsequent renewal of stimu- 

 lation, after fatiguing a muscle until it yields a contracture upon which 

 each new response appears merely as an augmentation of this state, to 

 observe this staircase phenomenon in a series of contractions, each 

 of which is obviously of a very prolonged, and therefore fatigued type. 

 Viewing the prolongation as symptomatic of a severe degree of fatigue, 

 it is inconceivable that muscle in this state should contract to a greater 

 degree save as the result of an increased excitation. It becomes 

 necessary therefore to consider the possibility that the nervous impulse 

 conveyed to the contractile material is modified by material within the 

 muscle, and that conduction through this material is quantitatively 

 facilitated by immediately antecedent use. The staircase phenomenon 

 is quite possibly an affair involving the concoplasm, and not the con- 

 tractile sarcostyles of muscle. In what degree a similar statement 

 is applicable, not only to the initial increase but also to the later fall in 

 the height of the contraction, remains an open question. 



In order to simplify the investigation of such points, I have directed 

 attention to the necessity for a connected conception of the facts of 

 muscular contraction, and in a paper published in the ' Quarterly Jour- 

 nal of Physiology ' I have endeavoured to supply a conception every- 

 where consonant with observed fact. According to the views there 

 advanced, the relaxation of muscle is an active process reversing the 

 conditions effective during contraction, and is to be regarded as a process 

 of recuperation tending to reconstitute in the muscle a state favourable 

 to the development of a subsequent contraction. 



The increased duration of the contraction of a fatigued muscle, 

 mainly but by no means entirely occupying the period of relaxation, is 

 capable of treatment as due to a diminished recuperative p^ ver. It is 

 of interest therefore to place alongside of this statement the fact 

 observed by all those engaged in the collection of measurements of 

 heat production in excised muscle, that when fresh and fatigued muscles 

 are made by adjustment of the stimulation to perform equal work 

 fatigued muscle gives off less heat. 



It is fair to assume that less combustion (i.e. , oxidation) has occurred 

 because the store of combustible material is becoming exhausted. As a 

 matter of fact, it has been shown that the presence of a smaller amount 

 of such material does actually, without reference to rest or fatigue, 

 diminish the amount of heat evolved during any standard contraction. 

 Temporarily, therefore, it may be said that a fatigued muscle performs 

 similar work, accompanied by diminished oxidation. It is absurd then 

 to regard oxidation as the prime cause of contraction. It is, on the 

 other hand, more probably a consequence of contraction, not so much 

 in the forefront during fatigue. In the paper quoted above I have 

 endeavoured to show that this is the case, and that oxidation, like 



