BY DR. MICHAEL FOSTER. 351 



strokes of the seeker, to free the muscle right up to its at- 

 tachment to the end of the femur, at h. The branch of the 

 sciatic nerve going to the gastrocnemius will be readily seen 

 when the muscle is turned over, as also another branch which 

 runs along its under surface, but which ends in other muscles. 

 Carefully avoiding any injury to the former nerve, but disre- 

 garding the latter, cut away the whole of the tibia and fibula 

 from the femur. Clear away, carefully avoiding the nerve, all 

 the" muscles of the thigh from the lower end of the femur so 

 as to leave the bone tolerably bare, and cut the bone across at 

 its lower third. There is left merely the end of the femur, to 

 which is attached the uninjured gastrocnemius, with the whole 

 length of the nerve from the muscle up to its entrance into 

 the spinal canal. The muscle attached to the fragment of 

 femur, with its prepared nerve, is represented in fig. 268. 

 (The vertebral fragment is not shown.) 



II. The Lever. In order to study the contraction of a 

 muscle, it is advantageous to employ a lever. 



The myographion of Helmholtz and Pfliiger is shown in fig. 

 269. The lever a moves on the fulcrum b and is balanced by 

 the counterpoise c. At d is either a fine brush to write on 

 paper, or a fine style to scratch smoked glass or paper. The 

 rod e bearing the style, moves on a hinge at/, and also carries 

 a counterpoise g. Hence the writing point describes a straight 

 line, while the actual end of the lever itself is describing the 

 arc of a circle. The silk thread coming from the tendon of 

 the muscle is attached at h. The small pan is to receive 

 weights for loading the muscle. 



For ordinary purposes, the simple lever .of Marey, shown in 

 the lower part of fig. 210, is much more convenient for use, 

 while at the same time the momentum of the heavy lever of 

 the myographion is avoided. The portion next to the fulcrum 

 is of metal, perforated or notched to receive the hooks, etc., 

 by which the muscle is attached above, and the weight below. 

 This is prolonged by a thin slip of wood or piece of straw, at 

 the end of which is a fine brush, placed horizontally at an 

 angle of about 60 degrees to the long axis of the lever, or a 

 thin slip of gutta-percha bearing a fine needle for tracing on 

 smoked glass or paper. 



To get rid of the momentum, the weight may be replaced 

 by a long weak spiral spring. This spring must be graduated 

 beforehand, i. e., the amount of force determined which is re- 

 quired to extend it to a given amount. The spiral may be 

 replaced by a simple slip of main-spring pressing on the lever 

 in a direction opposite to that of the movement given to it by 

 the muscle. 



III. The Moist Chamber. In order to prevent the 

 muscle and nerve from drying, they must be kept damp. 



