WORK OF MUSCLE : EXTENSIBILITY OF MUSCLE 



43 



30 grammes). Begin with the muscle free-weighted, and by using 

 the screw stop beneath the lever raise the latter so that the muscle 

 and connecting thread are somewhat slackened. Under these circum- 

 stances the muscle will not begin to raise the weight until its con- 

 traction has proceeded to a certain extent ; this shows the effect 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 or gastrocnemius 

 muscle and fix one end to a heavy disc of metal 

 provided with a hook : place the disc and muscle 

 in a beaker of Ringer's solution (Fig. 39). 

 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 to heat the beaker of 

 Ringer's solution, which should be provided 

 with a thermometer. Notice the effect of the 

 gradual rise of temperature upon the length of 

 the muscle as recorded by the lever. Note 



especially that at certain temperatures which 



J , .,, ,-, , .. FIG. 40. Experiment to 



correspond with the coagulation temperatures determine if a muscle 



of the muscle proteins there is a marked 



alters in volume dur- 

 ing contraction. a, 

 Muscle in Ringer's 

 solution ; &, capillary. 



shortening. (The final contraction corresponds 

 with the coagulation temperature of the colla- 

 genous matter, i.e., of the connective tissue, 

 and is not muscular). After no further shorten- 

 ing is produced, remove the flame and allow the liquid 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 now 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. 40). 

 Through the cork are passed a glass tube drawn out above the cork 

 to a capillary size, two copper wires of unequal length coiled spirally, 

 and each ending below in a sharp hook : above the cork each wire 

 ends in a loop. Fill the bottle to the rim with boiled and subse- 

 quently cooled Ringer's solution. Attach a fresh muscle by its two 



