1 86 



PRACTICAL PHYSIOLOGY. 



[XXXI 



muscle contracts, but does not elongate : it shows little tendency 

 to elongate unless it be weighted. 



5. Dead Muscle and Nerve. Immerse a nerve-muscle preparation for a 

 few minutes in water at 40 C. Both are killed, and none of the above 

 stimuli cause contraction. 



6. The Sartorius. One gets a clear idea of the shortening and thickening 

 which occur whtn a muscle contracts by using the sartorius, as its fibres are 

 arranged in a parallel manner. 



(a.) Pith a frog, lay it on its back, and dissect off the long narrow sartorius 

 from the inner side of the thigh. The thin narrow sartorius (fig. in) 

 stretching from the ilium to the tibia is best seen if it be moistened with 

 blood, which differentiates its edges. To isolate 

 the sartorius the best way is to cut the other 

 parts away from it. Raise its tibial tendon, and 

 round it tie a fine silk thread. Gradually raise 

 the muscle by means of the thread, and with fine 

 scissors cut it free from its fascial connections 

 right up to the ilium. Cut it out with the ilium 

 attached. Its nerve enters it on its under surface 

 about the middle of the muscle. When it is 

 divided the muscle contracts. Stretch it on a 

 slip of glass or hang it up by its ilium bony 

 attachment in a clamp. 



(b. ) Stimulate the muscle first at its ends and 

 afterwards at its centre or equator, as in Lesson 

 XXXI. 1, 2, with(i.), a single induction shock, 

 and (ii.), afterwards with an interrupted current. 

 Observe the shortening and thickening, which 

 are much greater in (ii. ) than (i. ). The muscle 

 may be extended again, and stimulated as 

 frequently as desired, if it be kept moist. 



FIG. in. Muscles of the Left 7. Unipolar Stimulation. Apparatus. 

 t L he^tnt. Fl g, g iTeo n ps f oaS Daniell's cell, induction machine, Du 

 *. Sartorius ; ad 1 . Adductor Bois keys, (muscle-chamber), wires, elec- 



longus; w.Vastus interims. , > 

 (See figs. 105 and 106.) trodes. 



A. (a.) Expose the sciatic nerve of a 



frog, and place the frog on a dry cork plate, or glass, or block of 

 paraffin. Arrange an induction apparatus for faradisation with the 

 electrodes short-circuited, and placed under the sciatic nerve clear 

 of all adjoining muscles. Open the short-circuit key and find a 

 strength of current (secondary coil at 25-30 cm.) which on 

 faradisation gives feeble tetanus. 



(/;.) Disconnect one of the electrode wires from the preparation, 

 so that only one terminal is in connection with the nerve. There 

 is no contraction when the secondary key is open. Insulate the 

 preparation by placing it on a block of paraffin or on a dry 

 beaker. 



(c.) Try to find the distance of the secondary coil (8-10 cm.) 



