PRACTICAL EXERCISES 621 



and put a pair of bulldog forceps on the anus. Fix the animal on a 

 holder as soon as the chloral has taken effect. Clip the hair from 

 the front of the neck and insert a tracheal cannula (p. 177). Now 

 inject subcutaneously enough of a i per cent, solution of curara to just 

 paralyze the skeletal muscles. As soon as symptoms of paralysis of 

 the muscles of respiration have appeared, connect the tracheal cannula 

 with the artificial respiration apparatus. Now expose the sciatic nerve 

 (p. 1 86) on one side, put on a ligature, and divide it above the ligature. 

 Lay the nerve on electrodes connected with the secondary coil of 

 an induction machine arranged for tetanus, and stimulate it If the 

 muscles supplied by the nerve contract, curara must be injected till 

 contraction is no longer obtained. Then the nerve is continuously 

 stimulated for a long time. After some hours the curara action will 

 begin to wear off, and it may be seen that the muscles of the leg 

 again contract. This shows that even a very prolonged stimulation 

 is not sufficient to exhaust the extra-muscular nerve-fibres (Bowditch). 



FIG. 193. ARRANGEMENT FOR STUDYING VOLUNTARY MUSCULAR. FATIGUE. 



13. Seat of Exhaustion in Fatigue for Voluntary Muscular Con- 

 traction. Support the arm, extensor surface downwards, on a rest 

 such as that shown in Fig. 193, and connect the middle finger of 

 one hand, by means of a string passing over a pulley on the edge 

 of a table, with a weight of 3 or 4 kilos. The string is attached to 

 the finger by a leather collar surrounding the second phalanx of the 

 finger, but allowing free movements of the joints. The extent of the 

 vertical movements of the string (and therefore the work done) may 

 be registered on a drum by a writing-point connected with it, the 

 whole arrangement forming what is called an ergograph. Two collar 

 electrodes (strips of copper covered with cotton-wool soaked in salt 

 solution, and bent to a circular form) are placed on the forearm, and 

 connected through a short-circuiting key with the secondary coil of an 

 induction machine arranged for tetanus (p. 175), and having a battery 

 of four or five Daniell cells, coupled in series,* in its primary circuit. 

 The middle finger is now made to raise the weight repeatedly by 

 vigorous contractions of the flexor muscles until at length a failure 

 * I.e., the copper of one cell connected with the zinc of the next. 



