GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 87 



Rate of Conduction. — The activity of the conduction process varies 

 greatly in differenl tissues. The nerves of* warm-blooded animals conducl more 

 rapidly than those of cold ; in a given animal the nerve-fibres conduct more 

 rapidly than muscle-fibres; striated muscle conducts more rapidly than smooth 

 muscle; and even within a single cell different portions may transmit the ex- 

 citing process at different rates ; thus the myoid substance of the contractile fibres 

 of one of the rhizopods conducts more rapidly than the less highly differen- 

 tiated protoplasm of the cell. In general, it may be said that, "the power to 

 conduct increases with increase of mobility and sensitiveness to external irri- 

 tants, a fact which reveals itself in the protozoa, by a comparison of the slowly 

 moving rhizopods with the lively flagellata and ciliata." 1 A study of different 

 classes of muscle-tissue supports this view. 



(a) Rate of Conduction in Muscles. — The conduction process is invisible, 

 hence we estimate its strength and rate by its effects. It is most readily fol- 

 lowed in such mechanisms as muscle, where the conducting medium itself 

 undergoes a change of form as the exciting influence passes along it. 



Rate of Transmission of ]\'ar<- of Contraction. — If a muscle be excited to 

 action by an irritant applied to one end, it does not contract at once as a whole, 

 but the change of form stalls at the point which is irritated and spreads thence 

 the length of the fibres. At the same time that the muscle shortens it 

 thickens, and under certain conditions the swelling of the muscle can be seen 

 to travel from the end which is excited to the further extremity. In the case 

 of normal, active, striated muscle, the rate at which the change of form spreads 

 over the muscle is far too rapid to be followed by the eye, and hence the 

 muscle appears to act as a whole. By suitable recording mechanisms, evidence 

 can be obtained of the rate at which the exciting influence and contraction pro- 

 cess pass along the fibre. Thus two levers can be so placed as to rest on the 

 two extremities of a muscle, at the same time that the free ends of the levers 

 touch a revolving cylinder, the surface of which is covered with paper black- 

 ened with lampblack. The writing-point of one lever must be directly under 

 the point of the other. If, when the cylinder is revolving, one end of the mus- 

 cle be stimulated, the record will 

 show that the lever resting on that 

 part is the first to move, making 

 it evident that that part of the mus- 

 cle begins to thicken first, and that 

 the contraction docs not begin al 

 the further extremity of the mus- 

 cle until somewhal later. The re- 

 cord given in Figure 33 was ob- 

 tained in a similar experiment, but 

 one in which the contraction of 

 the muscle was registered by the 



pince myographique and recording tambour of Many (see Fig. 34) 

 1 Biedermann: Eleklrophysiologie, 1895, Bd. i. S. 124. 



Fig. 3:i. — Rate of conduction of the contraction pro- 

 cess along ■■' muscle, as Bhown by the difference In the 

 tlmi of thickening of the t\\<> extremities. The tuning* 

 f«.rk waves record ,\„ second (after Marey), 



