CH. IX.] 



MYOGRAPHS 



93 



downstroke, and if the cylinder is travelling, the downstroke will 

 be written on a different part of the paper than the upstroke ; thus 

 a muscle curve or myogram is obtained. The paper may then be 

 removed, varnished, and preserved. 



Fig. 114 shows a somewhat different arrangement. 



The muscle is fixed horizontally on a piece of cork, B, one end 

 being fixed by a pin thrust through the knee-joint into the cork ; the 



FIG. 114. Arrangement of the apparatus necessary for recording muscle contractions with a revolving 

 cylinder carrying smoked paper. A, revolving cylinder ; B, the muscle arranged upon a cork- 

 covered board which is capable of being raised or lowered on the upright, which also can be moved 

 along a solid triangular bar of metal attached to the base of the recording apparatus the tendon of 

 the gastrocnemius is attached to the writing lever, properly weighted, by a ligature. The 

 electrodes from the secondary coil pass to the nerve being, for the sake of convenience, first of all 

 brought to a short-circuiting key, D (Du Bois Reymond's) ; C, the induction coil ; F, the battery 

 (in this fig. a bichromate one) ; B, the key (Morse's) in the primary circuit. 



tendo Achillis is tied to a lever which is weighted near its fulcrum : 

 the lever is so arranged that it rests on a screw till the muscle begins 

 to contract; the muscle therefore does not feel the weight till it 

 begins to contract, and gives a better contraction than if it had been 

 previously strained by the weight. This arrangement is called after- 

 loading. 



The writing surface is again a travelling cylinder tightly covered 

 with smoked glazed paper. The rest of the apparatus shows how 



