556 SELF-STIMULATION OF THE MUSCLE. 



The sciatic nerve is dissected out entire from the vertebral column to the knee ; the 

 muscles of the thigh separated from the femur, and the latter divided about its 

 middle, so that the preparation can be fixed in a clamp by the remaining portion 

 of the femur ; while the tendon of the gastrocnemius is divided near to the foot. 

 If a straw flag is to be attached to the foot, do not divide the tendo Achilles.] 



Rheoscopic Limb. The existence of a muscle-current may be proved without 

 the aid of a galvanometer : 1. By means of a sensitive nerve-muscle preparation 

 of a frog, or the so-called "physiological rheoscope" Place a moist conductor on 

 the transverse and another on the longitudinal surface of the gastrocnemius of a 

 frog. On placing the sciatic nerve of a nerve-muscle preparation of a frog on these 

 conductors, so as to bridge over or connect their two surfaces, contraction of the 

 muscle connected with the nerve occurs at once ; and the same occurs when the 

 nerve is removed. 



Make a transverse section of the gastrocnemius muscle of a frog's nerve-muscle 

 preparation, and allow the sciatic nerve to fall upon this transverse section ; the 

 limb will contract as the muscle-current from the longitudinal to the transverse 

 surface now traverses the nerve (Galvani, Al. v. Humboldt). These experiments 

 have long been known as " contraction without metals." 



[Use a nerve-muscle preparation, or, as it is called, a physiological limb. Hold the prepara- 

 tion by the femur, and allow its own nerve to fall upon the gastrocnemius, and the muscle will 

 contract, but it is better to allow the nerve to fall suddenly upon the cross section of the muscle. 

 The nerve then completes the circuit between the longitudinal and transverse section of the 

 muscle, so that it is stimulated by the current from the latter, the nerve is stimulated, and through 

 it the muscle. That it is so, is proved by tying a thread round the nerve near the muscle, when 

 the latter no longer contracts.] 



2. Self-Stimulation of the Muscle. We may use the muscle-current of an 

 isolated muscle to stimulate the latter directly and cause it to contract. If the 

 transverse and longitudinal surfaces of a curarised frog's nerve-muscle preparation 

 be placed on non-polarisable electrodes, and the circuit be closed by dipping the 

 wires coming from the electrodes in mercury, then the muscle contracts. Similarly 

 a nerve may be stimulated w T ith its own demarcation-current (du Bois-Reymond 

 and others). If the lower end of a muscle with its transverse section be dipped 

 into normal saline solution (0*6 per cent. NaCl), which is quite an indifferent fluid, 

 this fluid forms an accessory circuit between the transverse and adjoining longi- 

 tudinal surface of the muscle, so that the muscle contracts. Other indifferent 

 fluids used in the same way produce a similar result. 



[Kuhne's Experiment (fig. 402). The demarcation-current of the nerve of a 



nerve-muscle preparation may be used 

 as the stimulus to that nerve on com- 

 pleting the circuit. On an earthenware 

 bowl (B) is fixed a glass plate (G), and 

 thin rolls of modeller's clay (P P') are 

 bent over G. A nerve-muscle prepara- 

 tion is placed with its nerve (N) on the 

 clay, touching the latter with its trans- 

 verse and longitudinal surfaces. On 

 dipping the clay into a vessel containing 

 normal saline (C), the muscle contracts, 

 jrjg 402. and on withdrawing the normal saline, 



Kuhne's nerve demarcation-current experiment. lt a 8 ain contracts - In this case the 



nerve is stimulated by the completion 

 of the circuit of its own demarcation-current.] 



3. Electrolysis. If the muscle-current be conducted through starch mixed with 

 potassic iodide, then the iodine is deposited at the + pole, where it makes the starch 

 blue. 



