64 PHYSIOLOGICAL PHYSICS. [Chap. vir. 



a white cord passing down between the muscles. 

 Keeping he muscles separate, with the point of a 

 scalpel, by a slight stroke here and there, and without 

 touching the nerve, divide the fascia in which the nerve 

 is imbedded till it is completely shown from its 

 division just behind the knee-joint up to the place 

 where it disappears between ilium and coccyx. With 

 scissors cut through the ilium and the muscles of the 

 back above it, keeping well to the outer side, and, by 

 turning over the flap left connected with the vertebral 

 column, the nerves from which the sciatic is derived 

 will be seen. By clearing away the connective tissue 

 a long stretch of nerve from the lumbar region right 

 down to the knee is obtained. Reflect this stretch of 

 nerve over the gastrocnemius muscle ; then, holding 

 by the foot, with the scalpel scrape the femur clean of 

 muscle, and cut it through just below the head. 

 With the point of the scalpel pierce a small slit, to 

 admit the hook of the muscle telegraph, through the 

 tendo Achilles. Separate the tendon 

 from the foot below this, and by 

 pulling on the tendon separate the 

 gastrocnemius from the muscles below 

 it up to the knee. Snip through the 

 leg bones just below the knee, avoiding 

 all injury to the nerve. Thus there is 

 obtained the gastrocnemius M (Fig. 36), 

 with the long piece of nerve N at- 

 tached, the whole depending from the 

 Fig. 36. Nerve- femur F, by means of which the 



Muscle Pre- -, . -, ,-, ,. 



paration. muscle can be clamped in the torceps 



of the muscle telegraph, while the hook 

 of the telegraph can be passed through the opening 

 I in the tendon. 



Difference between continuous, inter- 

 rupted, and induced currents. This may be 

 studied with 'the aid of the muscle telegraph. Make 



