GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 77 



which follows the cutting off of the blood-supply. The working cell liberates 

 energy at the expense of its store of nutriment and oxygen, and through oxi- 

 dation processes forms waste products which are poisonous to its protoplasm. 

 The fatigue which results from functional activity has, therefore, a twofold 

 cause, the decrease in energy-holding compounds and the accumulation of 

 poisonous waste matters. 



It is evident that the length of time that the cell can continue to work will 

 depend very much upon the rapidity with which the energy-holding explosive 

 compounds are formed by the cell-protoplasm and the waste products are 

 excreted. If a muscle is made to contract vigorously and continuously, as 

 when a heavy weight is held up, fatigue comes quickly ; on the other hand, a 

 muscle may be contracted a great many times if each contraction is of short 

 duration and considerable intervals of rest intervene between the succeeding 

 contractions. The best illustration of this is the heart, which, though making 

 contractions in the case of man at the rate of seventy or more times a minute, 

 is able to beat without fatigue throughout the life of the individual. Each 

 of the vigorous contractions, or systoles, is followed by an interval of rest, 

 diastole, during which the cells have time to recuperate. The same is true of 

 the skeletal muscles. It was found in an experiment that if a muscle of the 

 hand, the abductor inditis, were contracted at regular intervals, a weight being 

 so arranged that it was lifted by the finger each time the muscle shortened, a 

 light weight could be raised at the rate of once a second for two hours and a 

 half, i. e. more than 9000 times, without any evidence of fatigue. If, however, 

 the weight was increased, which required a greater output of energy, or if the 

 rate of contractions was increased, which shortened the time of repose, the mus- 

 cle fatigued rapidly. In general, the greater the weight which the muscle has 

 to lift, the shorter must be the periods of contraction in proportion to the inter- 

 val of rest if the muscle is to maintain its power to work. Maggiora, 1 in his 

 interesting experiments in Mosso's laboratory at Turin, made a very careful study 

 of this subject, and ascertained that for a special group of muscles there is for 

 each individual a definite weight and rate of contraction essential to the accom- 

 plishment of the greatest possible work in a given time. Either increasing 

 the weight or the rate of contraction hastens the coming on of fatigue and so 

 lessens the power and the total amount of work. In such an exercise as 

 walking the muscles are not continually acting, but intervals of rest alternate 

 with the periods of work, and the time for recuperation is sufficiently long to 

 permit the protoplasm of the muscle-cells to prepare the chemical compounds 

 from which the energy is liberated, as fast as they are used, and get rid 

 of the waste products of contraction, so that vigorous muscles can be em- 

 ployed many hours before any marked fatigue is experienced. Sooner 

 or later, however, the vigor of the muscle begins to decrease. The reason 

 for this is not wholly clear. It is noticeable, however, that not only the 

 muscles employed in the work, but other muscles, such as those of the 

 arms for instance, even when purposely kept quiet, have their irritability 

 1 Archiv fur Anatomie und Physiologic, 1890 ; physiologische Abtheilung, p. 191. 



