130 



PHYSIOLOGICAL PHYSICS. 



[Chap. XII. 



brass plate, pivoted at a and a', is a lever which 

 rests at the other end on the plate by means of two 

 screw points, q and p. The screw point p is of 

 platinum, and rests on an insulated plate of platinum 

 fixed to the table ; the point of the screw q is of 

 amalgamated copper, and dips into a little insulated 

 cup containing mercury. Connected with p and q, 

 and insulated from the table, are the screws k and A'; 

 the latter screw in communication with p, the former 

 with q. A muscle, supported in the forceps, is 

 directly suspended over the lever, and is attached to 

 it by an insulating piece of tortoise-shell. Opposite 

 to this attachment, on the under side of the lever, is 

 connected a rod, which passes through a hole in the 

 table, and supports a scale for weights. If the muscle 



be stimulated it will lift 

 the lever against the 

 resistance of the weight, 

 but so long as the lever 

 rests on the table the 

 weight does not affect the 

 muscle. 



Now, suppose the 

 two wires from a con- 

 stant battery led to h' 

 and k. Let the current 

 pass by A', it will pro- 

 ceed to the platinum plate 

 in connection, thence by 

 p along the lever to g, 

 down through q to the 

 mercury cup, thence to k, 

 and back to the element. 



If the lever be raised by the contraction of the 

 muscle, the current will be interrupted by the 

 breaking of contact at p and q. In this circuit 

 h interposed a galvanometer G, a key K, and the 



Fig. 67. Arrangement of Frog-In- v "e>" / 



teiTupter and Galvanometer. 



