Chap, vii.] DIRECT STIMULATION. 67 



strongly that it is thrown into TETANIC CONTRACTION. 

 In other words, it has not time to relax after one 

 contraction before another shock is received. The 

 contraction is therefore continuous, and the muscle is 

 rigid. In all these experiments the current has been 

 sent through the muscle itself. This is called DIRECT 



o 



STIMULATION OF MUSCLE. The same experiments 

 should be repeated, using INDIRECT STIMULATION, that 

 is, stimulating through the nerve. For this purpose 

 detach the wires going to the forceps and the hook of 

 the telegraph, and attach them to the binding screws 

 of the platinum electrodes (Fig. 34). By means of a 

 camel-hair pencil, moistened with saliva, lift the nerve 

 hanging from the muscle preparation, and adjust it 

 over the points of the electrodes, the muscle being 

 secured in the telegraph as before. Let the nerve be 

 kept from drying by being moistened with saliva by 

 the brush. See that the nerve touches each electrode. 

 The space between the two points of contact should 

 be small. The nerve may in this way be stimu- 

 lated as the muscle was. 



Difference between direct and indirect 

 stimulation. Make a muscle -nerve preparation, 

 fix it in the telegraph, and stretch the nerve over the 

 platinum electrodes, or use the moist stimulation 

 tube (page 61). Connect a Daniell's cell with the 

 screws of the inductorium, so as to give single induc- 

 tion shocks, and interpose a simple key, as described 

 on page 57. Take the wires from the secondary coil 

 to cups 1 and 2 of the commutator (Fig. 33). From 

 cups 3 and 4 take two wires, and, for the sake of dis- 

 tinction, let them be covered with, say, red-coloured in- 

 sulating material, and connect them with the forceps 

 and the hook of the telegraph, so that the currenb will 

 stimulate directly. From cups 5 and 6 connect green- 

 covered wires to the electrodes, so that the current 

 will stimulate indirectly. Take out the cross of the 



