712 



A MANUAL OF PHYSIOLOGY 



made t6 vibrate. Let the drum off, set the spring vibrating by 

 depressing it with the finger, then open the key in the secondary. 

 The* muscle is thrown into incomplete tetanus, and the writing- 

 point traces a wavy curve at a higher level than the abscissa line. 

 Close the short-circuiting key, and the lever falls to the horizontal. 

 Repeat the experiment with the spring fastened, so that only f , ^, , 

 \ of its length is free to vibrate. The rate of interruption of the 

 primary circuit increases in proportion to the shortening of the 

 spring, and the tetanus becomes more and more complete till 

 ultimately the writing-point marks an unbroken straight line. Put 

 on a time-tracing by means of an electro-magnetic marker connected 

 with a metronome beating seconds or half-seconds (Fig. 76, p. 179). 

 (For specimen curves, see Fig. 247, p. 657.) 



16. Contraction of Smooth Muscles (ij Spontaneous Rhythmical 

 Contractions. Immerse in oxygenated Ringer's solution a ring of 



O3sophagus ob- 

 tained immediate- 

 ly after death from 

 a cat, or, still bet- 

 ter, from a chicken. 

 Use the arrange- 

 ment described on 

 p. 1025. Inthecase 

 of the cat's oeso- 

 phagus the ring 

 should be taken 

 from the lower half 

 of the O3sophagus, 

 since the upper por- 

 tion contains purely 

 striated muscle. 

 Obtain tracings 

 of the rhythmical 

 contractions on 

 a slowly - moving 

 drum (Fig. 264). 



(2) Fix one end 

 of a piece of cat's 

 oesophagus, 2 to 5 

 centimetres long, 

 to a muscle-clamp 



in a moist chamber, and the other end to- a lever writing on a drum. 

 Connect thin copper wires from the secondary coil of an inductorium 

 with the two ends of the piece of oesophagus. Take tracings to show 

 (a) the curve of a single contraction caused by a single make or break 

 shock, with estimation of the latent period, as in Experiment 12, 

 p. 710; (b) summation, as in Experiment 13, p. 711; (c) genesis of 

 tetanus, as in Experiment 15, p. 711; (d) the relations between strength 

 of stimulus and amount of contraction. For this last experiment 

 the drum should be stationary while the contraction is being recorded, 

 and should be allowed to move a little between successive con- 

 tractions. Begin with the secondary at such a distance from the 

 primary that a contraction is just caused by a break shock. Then 

 gradually increase the strength of the stimulus (always using the 

 break) till maximum contraction is obtained. The gradual increase 

 in the response is very clearly seen with the oesophageal preparation 

 (Waller) . 



FIG. 263. ARRANGEMENT FOR TETANUS. 



A, upright with notches, in which the spring S is 

 fastened (shown in section) ; C, horizontal board to which 

 A is attached, and in a groove in which the mercury-cup 

 E slides. The primary coil P is connected with E, and 

 through a simple key, K, with the battery B, the other 

 pole of which is connected with the end of the spring. 

 The wires from the secondary coil, P', go to a short- 

 circuiting key, K', from which the wires F go off to the 

 electrodes. 



