GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. Ill 



than the absolute contraction of the muscle. The part of the myogram cor- 

 responding to the height of the contraction of the muscle can be distinguished 

 from that due to the throw of the lever by a method suggested by Kaiser. 1 

 If the rising lever strikes a check, it remains in contact with the check as 

 long as the muscle continues to contract, but falls immediately if not held 

 there by the contraction process. By varying the height of the check, the 

 point corresponding to the true contraction height can be ascertained. 



(3) The fall of the curve may be altered.' The weight, suddenly freed by the 

 rapidly relaxing muscle, may acquire a velocity in falling which will stretch 

 the muscle-tissue, carry the record lower than the actual relaxation of the 

 muscle would warrant, and lead to the development of artificial elastic after- 

 oscillations. It must not be supposed, however, that the relaxation of the 

 muscle is merely a passive affair, and that it returns to its original shape 

 because, when it ceases to develop energy, it is stretched by the weight. The 

 relaxation, like the contraction process, is an active event, and it is antago- 

 nistic to the contraction process. 2 



These sources of error can be in part overcome by the employment of an 

 exceedingly light, stiff writing-lever, and by bringing the necessary tension on 

 the muscle by placing the extending weight very near the axis of the lever, so 

 that it shall move but little and hence acquire little velocity. 



(c) Effect of Rate of Excitation on Height and Form of Muscular Contrac- 

 tion. — If a muscle be excited a number of times by exactly the same irritant 

 and under the same external conditions, the amount and course of each of 

 the contractions should be exactly the same, provided the condition of the 

 muscle itself remains the same. The condition of the muscle is, however, 

 altered every time it is excited to contraction, and each contraction leaves 

 behind it an after-effect. This altered condition is not permanent; as we have 

 seen, increased katabolism is accompanied by increased anabolism, and, if the 

 excitations do not follow each other too rapidly, the katabolic changes occur- 

 ring in contraction are compensated for by anabolic changes during the suc- 

 ceeding interval of rest. Normally, a muscle, under the restorative influence 

 of the blood, rapidly recovers from the alterations produced by the contraction 

 process, and, therefore, if not excited too frequently, will give, other things 

 being equal, the same response each time it is called into action. The lust 

 illustration of this is the heart, which continues to beat at a regular rate 

 throughout the life of the individual. Tiege] found that one of the skeletal 

 muscles of a frog, while in the normal body, can make more than a thousand 

 contractions in response to artificial stimuli without showing fatigue; finally 

 the effect of the work shows itself in a lessening of the power to contract. 

 Every muscle contains a surplus of energy-holding compounds and also sub- 

 stances capable of neutralizing waste products, and even a muscle which has 

 been separated from the rest of the body retains tor a considerable time the 

 ability to recover from the effects of excitation. It is evident that when a 



1 Kaiser: Zeitechrift far Biologic, 1896, xxxiii. S. 157, 360. 



2 Fick, v. K rifs, and others 



