THE STUDY OF MUSCLE PHYSIOLOGY. 



199 



are increased — i. e., the metabolism and the working tension 

 are related. 



These experimental facts harmonize with our experience of 

 a sense of satisfaction and effectiveness in the use of the muscles 



r-rT'T' 



TTn'-r-rn-i- 



10 2U 3D 10 45 so 55 60 65 70 



•75 



80 90 100 



Pig. 183.— Di^am of mnscular contractions with same stimulus and increasing 

 weights. The numbers represent grammes (McKendriclt). 



when weights are held in the hands ; and it must be a matter 

 of practical importance that each person should, in taking sys- 

 tematic exercise, keep to that kind which does not either over- 

 weight or underweight the muscles. 



OmOUMSTANOES INFLUENCING THE CHARACTER 

 OF MUSCULAR AND NERVOUS ACTIVITY. 



The Influence of Blood-Supply. Fatigue.— Fig. 184 shows at 

 a glance differences in the curves made by a contracting muscle 

 suffering from increasing fatigue. 



180 DV. 



Fig. 184.— Curves of a muscle contraction in different stages of fatigue (after Tec). 

 A, curve when muscle was fresh; S, C, D, E, each just after muscle had already 

 contracted two hundred times. The alteration in length of latent period is not 

 well brought out in these tracings. 



Suppose that in such a case the blood had been withheld 

 from the muscle, and that it is now admitted, an almost im- 

 madiate effect is seen in the nature of the contractions ; but 

 even if only saline solution had been sent through the vessels of 

 the muscle, a similar change would have been noticeable. We 

 may fairly conclude that the blood and saline removed some- 

 thing which had been exercising a depressing effect on the 

 vitality of the muscle. In a working muscle, like all living 

 tissues, there are products of vital action (metabolism) that are 

 poisonous. We have already learned that a working muscle 

 generates an excess of carbonic anhydride, and something which 

 gives it an acid reaction ; and that it uses up oxygen as well as 

 other matters derivable from the blood. 



