126 THE MYOGRAPH. 



10. Chemical Excitation. Make a nerve-muscle preparation. Place 

 it on a card, having a hole in the middle just large enough to allow the nerve 

 to pass. Place the card, with the nerve hanging from it, over a beaker con- 

 taining ammonia. The muscle does not contract. Then cut off the nerve 

 and expose the muscle to the'gas. It contracts. Glycerine, on the other hand, 

 excites nerve readily, but scarcely acts on muscle. 



11. Action of the Arrow Poison (Curare) on Muscle 



and Nerve- In a preparation of which the hemispheres have been 

 destroyed, pass a ligature under the sciatic nerve above one knee and tighten 

 it so as completely to arrest the circulation beyond. Inject a drop of a solu- 

 tion containing o'l per cent of curare under the skin and leave the preparation 

 in a moist chamber for an hour. Then test the condition of the muscles by 

 direct excitation and excite both sciatic nerves, comparing the effects. Although 

 both have been equally acted upon, it is on the ligatured side only that the 

 excitation is responded to. The experiment shows that the arrow poison acts 

 neither on nerve trunks nor on muscular tissue but only on the muscular 

 nerve-endings. 



II. The Myograph. 



Any instrument by which a curve can be drawn which truly represents the 

 contraction of a muscle is called a myograph. 



I. The most simple myograph is that of Marey, the construction of which 

 is as follows : A pillar, supported by the horizontal triangular bar of the record- 

 ing apparatus (kymograph), carries a board seven inches long by two and a 

 half in width, which with the aid of a rack-and-pinion and adjusting screw, 

 can be moved either vertically or horizontally. At one end of the board is a 

 vertical pillar on which a writing lever is supported ; the point of the lever 

 can be brought into such a position as to inscribe its movements on the 

 revolving cylinder. The lever is centred on a horizontal axis, its motion being 

 resisted by a delicate spring. The upper surface of the board is covered to 

 within a short distance from the lever, with a thick plate of cork. (See 

 " Handbook," fig. 270 bis.) 



Various muscles of the frog are used for myographic purposes ; the one 

 most easily prepared is the gastrocnemius. All that is required is to divide 

 the skin so as to expose the tendon, and to attach the latter to a strong liga- 

 ture thread. A strong needle must now be thrust through the end of the 

 femur without injuring other parts, so as to fix the femoral attachment of the 

 muscle to the cork plate in such a position that the ligature may be advan- 

 tageously fastened to the lever. 



Arrange the apparatus for single induction shocks as directed in Section I., 2, 

 interposing in the primary circuit an additional key, which is so placed as to be 

 opened by the recording cylinder on arriving at a certain part of its revolution. 



Cover the cylinder smoothly and tightly with glazed paper, taking care that 

 the edge of the crease does not catch the writing style. Smoke the surface 

 xiniformly with a paraffin lamp and put the cylinder on the middle axis. 



Place the electrodes on the tongue and set the clock in motion, so as to 

 ascertain that the electrical apparatus is working properly. 



