i 7 8 



PHYSIOLOGICAL PHYSICS. [Chap. xvn. 



produced by the movement. The muscle is stimulated 

 indirectly. The figure shows two platinum wires 

 supported in a piece of vulcanite, the wires being in 

 connection with two little mercury cups. The vul- 

 canite is connected by a piece of flexible lead tube to 



Fig. 88. Marey's Myographion. 



a brass support springing from the frog-plate. The 

 extremity of each wire is bent into a fine hook. A 

 slit is made in the skin of the thigh of the frog, and 

 the muscles are separated just sufficiently to show the 

 sciatic nerve. The wires are then placed under the 

 nerve by means of their hook-like extremities. The 

 nerve is therefore very little disturbed. Into each 

 mercury cup is put a wire from the secondary coil of 

 an induction machine ; by this means, the small 

 piece of nerve between the two platinum electrodes is 

 stimulated. The primary coil of the inductorium 

 may be arranged to give a single shock (page 65), or 

 for the production of tetanus, and the lever will 

 accordingly give the curve of a single contraction or 

 of tetanus, revealing the characteristics of contraction 

 and relaxation in each case. As seen in the figure, the 



