GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 71 



cause, the decrease in energy-holding compounds available for work 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 indicis, 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. These experiments 

 were made on men, and the height of the succeeding contractions was re- 

 corded by an apparatus devised by Mosso, the ergograph, 2 which made it 

 possible to estimate the total amount of work done by the muscles studied. 

 Many forms of apparatus have since been devised to accomplish this. 

 Mosso's ergograph consisted of two parts, an arm rest equipped with suitable 

 clamps for fixing the arm and hand, and a writing mechanism arranged to 

 record the movements of the weight which was raised hv the flexion of 

 the second linger. Either increasing the weight or the rate of contrac- 

 tion 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 t<> prepare the chemical compounds from 

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



1 Archiv fiir Anatomie uittl Physiologie, 1890; physiologische Abtheilung, S. 191. 



2 Mosso: Die Ermiidung, Leipzig, 181*2, S. '.hi ; Lombard: Journal of Physiology, 1892, vol. 

 xiii. Fig. 1, Plate 1. 



