WORK OF MUSCLE; EXTENSIBILITY OF MUSCLE 



41 



of after-loading. Describe a series of contraction ordinates with a 

 gradual increase of after-load. Calculate the amount of work done 

 under these conditions, and compare with that performed by the free- 

 weighted muscle. 



Effect of heat on the extensibility Of muscle. Take a sartorius muscle and fix 

 one end to a heavy disc of metal provided with a hook : place the disc and muscle 

 in a beaker of Ranger's solution (fig. 38). Attach the other end of the muscle by 

 means of a thread to the short arm of a lightly weighted lever of the first order, so 

 that when the muscle shortens the long arm of the lever is raised. Let the point 

 of the lever write on a very slowly moving drum. Arrange a small gas or spirit 

 flame under the beaker and slowly heat the Ringer's solution, which shouldfbe 

 provided with a thermometer. Notice the effect of the gradual rise of tempera- 

 ture upon the length of the muscle as recorded 

 by the lever. Note especially that at certain 

 temperatures which correspond with the coagu- 

 lation temperatures of the muscle proteins there 

 is a marked shortening. (The final contraction 

 corresponds with the coagulation temperature of 

 the collagenous matter, i.e. of the connective 

 tissue, and is not muscular.) After no further 

 shortening is produced, remove the flame and 

 allow the Ringer to cool. There is no reversal of 

 the contraction of the muscle, which remains stiff 

 and completely coagulated (heat rigor). If the 

 muscle is cut and tested with litmus paper it will 

 be found to be acid. 



During contraction a muscle does not alter in 

 volume. Take a wide-mouthed bottle with well- 

 fitting paraffined cork (fig. 39). Through the cork 

 are passed (a) a glass tube drawn out above the 

 cork to a capillary size ; (6) two copper wires of 

 unequal length coiled spirally, and each ending 

 below in a sharp hook : above each terminates in 

 a loop close to the cork. Fill the bottle to the 

 rim with Ringer's solution. Attach a fresh muscle 

 by its two ends to the hooks, lower into the 



bottle, and press the cork in securely : the fluid FIG - 39. EXPERIMENT TO DETER- 

 should completely fill the bottle and capillary to 

 the exclusion of air-bubbles. Draw a little of the 

 fluid out of the capillary by filter paper, and mark 

 the level at which the fluid then stands. Hook 



wires from the secondary coil to the loops above mentioned, and tetanise the 

 muscle. If there were a diminution of volume the level of the water in the 

 capillary would fall. 



Preparation of the sartorius muscle. The thin, flat sartorius is seen crossing 

 obliquely over the front of the thigh. It is readily isolated by tying a thread 

 round its tendinous attachment to the tibia, cutting this attachment away from 

 the bone, raising the lower end by the aid of the thread, and snipping through 

 the fascia on either side of the muscle, thus separating it right up to its iliac 

 attachment. Notice the twitch which occurs when the nerve, which enters 

 the under surface about its middle, is cut through. The muscle may be left 

 attached to the ilium, or its bony attachment may be cut away with it and the 

 muscle thus completely isolated. Its uppermost part contains no nerve fibres, 

 and can be used to show that, independently of nerve, muscle responds to all 

 forms of stimulation (electrical, mechanical, thermal, and osmotic). 



MINE IP A MUSCLE ALTERS IN 

 VOLUME DURING CONTRACTION. 

 a, MUSCLE IN RINGER SOLUTION; 

 6, CAPILLARY. 



