258 PHYSIOLOGY 



These time-relations vary with the temperature of the muscle. We 

 have already seen that the effect of lowering the temperature is to 

 increase the latent period of the contraction. In the same way it 

 slows the rise of the electrical change and the rate of propagation 

 of the wave of electrical change. This is shown in Fig. 87, in which 

 are given the diphasic response of the sartorms first at 8 

 secondly at 18 C. We are therefore justified in regarding the electrical 



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change as an index to the chemical changes evoked in the muscle 

 as the direct result of the stimulus. The flow of material, which i 

 responsible for the change in form of each contracting unit, is secondary 

 to these changes. As the result of stimulation, a chemical change 

 aroused at the point of excitation and travels thence along the muscL 

 fibres at a rate of about three metres per second, i.e. the same rate 

 as that of the following waye of mechanical change, and, like 

 varying with the temperature. Under certain conditions an excita. 

 tory condition may be propagated without the presence of a visible 

 contraction, Thus, if the middle third of the sartonus be soaked 



