50 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



(1) If a sufficient interval is allowed between contractions no fatigue 

 is apparent. With a load of 6 kilograms, for instance, the flexor 

 muscle (M. flexor digitorum suUimis) showed no fatigue when a 

 rest of 10 seconds was given between contractions. (2) After 

 complete fatigue with a given load a very long interval (two 

 hours) is necessary for the muscle to make a complete recovery 

 and give a second record as extensive as the first. (3) After 

 complete fatigue efforts to still further contract the muscle 

 greatly prolong this period of complete recovery, a fact that 

 demonstrates the injurious effect of straining a fatigued muscle. 

 (4) The power of a muscle to do work is diminished by conditions 

 that depress the general nutritive state of the body or the local 

 nutrition of the muscle used; for instance, by loss of sleep, 

 hunger, mental activity, anemia of the muscle, etc. (5) On the 

 contrary, improved circulation in the muscle produced by 

 massage, for example increases the power to do work. Food 

 also has the same effect, and some particularly interesting 

 experiments show that sugar, as a soluble and easily absorbed 

 foodstuff, quickly increases the amount of muscular work that 

 can be performed. (6) The total amount of work that can be 

 obtained from a muscle is greater with small than with large loads, 

 since fatigue sets in more rapidly with the larger loads. (7) 

 Marked activity in one set of muscles the use of the leg muscles 

 in long walks, for example will diminish the amount of work 

 obtainable from other muscles, such as those of the arm. It is 

 very evident that the instrument may be used to advantage in the 

 investigation of many problems connected with gymnastics, diet- 

 etics, stimulants,* medicines, etc. 



A point of general physiological interest that has been brought out in con- 

 nection with the use of the ergograph calls for a few words of special mention. 

 Mosso found that if a muscle e. g., the flexor digitorum sublimis is stimu- 

 lated directly by the electrical current and its contractions are recorded by. 

 the ergograph, it will give a curve similar to that figured above for the volun- 

 tary contractions, except that the contractions are not so extensive. Under 

 these conditions the muscle, when completely fatigued to electrical stimula- 

 tion, will respond to voluntary stimulation from the nerve centers. On the 

 other hand, after fatigue from a series of voluntary contractions it has been 

 observed that the muscle will still give contractions if stimulated directly by 

 electricity. It is stated, in fact, that one can alternate a number of times from 

 voluntary to electrical stimulation, the fatigue induced by one method giving 

 place to a series of contractions when the other method of stimulating the 

 muscle is employed. It follows from these facts that the fatigue, as observed 

 in voluntary contractions, is not a fatigue of the muscles themselves, but 

 rather of some other part of the neuromuscular apparatus. In this apparatus 

 we have to consider a number of elements: the cortical nerve cells of the cere- 

 brum, the spinal nerve cells, the synapse or synapses connecting these neurons, 



*Schumberg, "Archiv f. physiol.," 1899, suppl. volume, p. 289, and 

 Palmen, " Skandinavisches Archly fur Physiologic," 1910, 24, 168, 197. 



