306 PRACTICAL PHYSIOLOGY 



out of position along the finger. In this way take 300 to 600 con- 

 tractions on a drum revolving at an extremely low rate (Fig. 183). 



At first sight the most striking feature of the curve is the more or 

 less rhythmical waxing and waning in the height of the contractions; 

 this seems to be purely central in origin and to be due to variations in 

 the strength of the voluntary impulse communicated to the muscle. 

 Practice to a large extent does away with this rhythm. When the 

 height of the contraction is measured it will be found that the average 

 height decreases during the first 180 contractions and then attains a 

 fairly constant level, which represents about 85 per cent, of the height 

 of the original contractions. The initial decrease is better marked in 

 Fig. 184, and here the fatigue-level was only about 45 per cent, of the 

 original height. The characteristics of an ergographic fatigue-curve, 

 therefore, are an initial fall which takes place during a variable number 

 of contractions, and the attainment of a fairly constant level, which 

 represents varying percentages of the height of the original con- 

 tractions. This curve strongly suggests that during a series of con- 

 tractions two processes are at work ; one by which available combustible 

 material is being used up and the products of katabolism are accumu- 

 lating, and the other by which both these defects are made good by the 

 circulation. During the early part of the curve the first process 

 preponderates over the second and the height of the contraction 

 decreases, but as soon as the two processes exactly balance each other 

 a uniform level is maintained for hundreds of contractions. The 

 probable seat of these processes will be referred to after the next 

 experiment has been performed. 



In order to obtain a record of the contractions of the gastrocnemius 

 with its circulation intact, arrange the apparatus for stimulating the 

 sciatic nerve with maximal induction shocks, using a simple key in the 

 primary circuit. The cerebrum of the frog must be destroyed and the 

 muscle-nerve preparation made without causing bleeding. The cerebral 

 hemispheres are destroyed by compression, leaving the medulla and spinal 

 cord intact, and the gastrocnemius is prepared in the usual way. A string 

 ligature is placed beneath the gastrocnemius and tied tightly round the 

 upper part of the tibio-fibula and the remaining muscles ; the leg is 

 then cut through below the ligature. The whole frog is placed belly 

 downwards on the myograph-board, a strong pin is pushed through the 

 lower end of the femur and driven firmly into the cork. A piece of 

 moistened flannel is then pinned down over the trunk to prevent the 

 contractions of the muscles of the trunk from disturbing the lever 

 connected with gastrocnemius. The skin over the middle of the thigh 

 is divided longitudinally for a short distance, the muscles carefully 



