28 EXPERIMENTAL PHYSIOLOGY. 



connect the binding post of the lever to the tendon by means 

 of a fine wire. 



With the muscle under some tension secure a record of a 

 single contraction upon the drum of the spring-driven kymo- 

 graph. 



Secure a second record with an increase in tension. Record 

 an iso tonic curve by means of the other lever on the tripod. 

 Stimulation signals and tuning fork records must be shown 

 under each record. 



In order to obtain the tension or resistance overcome by the 

 muscle in the isometric contraction, turn the spring over and 

 attach the large scale-pan (weight 20 grams). Then add 

 sufficient weights to stretch the spring to the same extent as 

 occurred in the isometric contractions. Turn the drum by 

 hand to make short abscissae. Mark these lines with the 

 weights. (May also be done with Harvard kymograph as in 

 Exp. 8a). 



Compare the latent periods, contractions and relaxations in 

 the isometric and isotonic records. 



It is never possible to obtain a purely isotonic contraction, for 

 in all contractions of this kind, tension does change, though ever 

 so little. Nor does the purely isometric type exist, in spite of the 

 fact that the muscle does not lift its load and thus appears to be 

 free from any shortening of fibres. Watch such a muscle at work. 

 Some of the fibres do thicken at least in part of their course, there- 

 fore they must shorten. They probably do so at the expense of a 

 slight extension of the tendon or of other fibres. 



Throughout the activity of the muscles of the body we may 

 have contractions predominantly isotonic or predominantly iso- 

 metric or these may be combined in various proportions. 



EFFECT OF TEMPERATURE ON CONTRACTION. 



Chemical, changes underlie muscle activity. All chemical pro- 

 cesses are influenced by temperature, a rise causing an increase 

 in the rate of the reaction, a fall causing a decrease. Within 

 certain limits we find this true in muscle. There is this difference 

 from inorganic chemical processes the maximum reaction is soon 



