52 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



Spin drum very rapidly. Only the initial rise of the curve is required. 

 Take another twitch with the key rocked over to stimulate through the 

 near electrode. Measure the distance between the two electrodes and 

 record this distance on kymograph. Observe the time difference between 

 the two latent periods. Calculate the rate of transmission of the impulse 

 in metres per second (cf. Howell, 12th Ed., p. 117). Estimate the 

 chronaxie of this nerve. The impulse travels one cm. in one chronaxie. 

 Cf. Lapicque, L'Excitabilite, 1926, p. 356. Discuss the speed of impulses 

 in various nerve fibres. The rapidity of the various fibres in a nerve 

 depends on their irritability and diameter. Helmholtz first measured the 

 rate of a nerve impulse (Arch. Physiol., 1850, p. 71). Cf. Mitchell, 

 1932, Fig. 11, p. 23. Text p. 344. 



20. Augmentation of Muscular Chronaxie. — Attach a sciatic-gastroc- 

 nemius preparation to the myograph lever in the usual way. Apply 

 one pair of electrodes to the nerve and another pair, composed of fine wire, 

 to the muscle. The electrodes are connected by a rocking key. Arrange 

 the switch to excite through the nerve and stimulate with a simple key 

 once per second with the drum moving slowly and the muscle lifting thirty 

 grams at each contraction. Record the contractions until the muscle 

 ceases to raise the weight. Then rock over the key to stimulate the muscle 

 directly and record the contractions again until fatigue is complete. 

 Fatigue increases the muscle chronaxie and conduction from the nerve is 

 blocked. (Heterochronism.) Cf. Lapicque, "L'Excitabilite," p. 278. 

 For recent views on chronaxie cf. Davis and Forbes, Physiol. Rev. 16: 

 407, 1936. Text p. 358. 



21. Contraction of Hyoglossal Muscle (Red Fibres). — Remove whole 

 lower jar and hyoid cartilage with tongue attached from frog used for 

 gastrocnemius studies. Tie a thread to the tip of the tongue and fix the 

 hyoid with pin to a slice of cork held in a femur clamp. The tongue 

 may pull vertically on the lever (not weighted). Stick electrodes into 

 muscle just in front of hyoid. Take a simple twitch with signal key 

 and tuning fork. Compare latent period and duration of contraction 

 with those obtained with gastrocnemius (white fibres) (cf. Ranvier, 

 Comp. rend. Acad. Sci. Paris, 77: 1030, 1873; Hinsey, Physiol. Rev., 14, 

 565, 1934). Text p. 318. 



22. Contraction of Smooth Muscle. — Make two transverse cuts across 

 a frog's stomach to obtain a ring of smooth muscle about 5 mm. wide. 

 Place in Ringer until relaxation occurs. Fasten a fine wire to inductorium 

 and bend up at end. Clamp at bend and fasten the end through the ring 

 of muscle. Fasten a straight fine wire to the other part of the induc- 

 torium, bend last 2 ins. down and fasten through ring of muscle. Attach 

 elbow of upper wire with thread to a heart lever. Stimulate with a 

 strong shock or tetanizing current. Compare curve with those from 



