73 6 THE PHYSIOLOGY OF THE CONTRACTILE TISSUES 



Thus, according to Piper, the total number oi simple discharges, 

 each associated with an electrical change in the muscle, as recorded by 

 the string galvanometer, is 47 to 50 a second. The rhythm of strych- 

 nine tetanus in the frog is about 8 to 12 per second. By means of the 

 capillary electrometer (p. 702) large electrical oscillations at this rate 

 can be demonstrated, each of which represents a short tetanic spasm, 

 as is shown by the fact that a number of smaller electrical oscillations 

 are superposed upon the large ones (Sanderson). The electrical changes 

 suggest that each discharge causes a simple contraction much more 

 prolonged than the twitch of a directly stimulated muscle. This 

 removes the difficulty of understanding how such a small number as 

 10 contractions per second could be smoothly fused, and indicates that 

 even the shortest possible voluntary movement, which can be executed 

 j n JL. to ^j of a second, is not caused by a single impulse, but is a 

 tetanus. For these brief movements the frequency of oscillation, as 

 shown by the action currents, is the same as for sustained contractions. 

 The electrical changes in the voluntarily contracted muscle seem to 

 differ in amplitude or abruptness from those produced in experimental 

 tetanus. For secondary tetanus (p. 806) is not caused by muscle in 

 voluntary contraction. But this is also the case with the other pro- 

 longed contractions caused by continuous artificial stimulation e.g., 

 Ritter's tetanus (p. 715) and the contraction produced by sodium 

 chloride or ammonia. We need not hesitate to conclude, then, that 

 the voluntary contraction is discontinuous, in the sense that it is not 

 a perfectly smooth and uniform tonic contraction, although we still 

 lack a decisive proof that it is maintained by a strictly intermittent 

 outflow of nervous energy, and not by a continuous outflow causing a 

 sustained contraction, which, it may be, remits and is reinforced at 

 intervals. The apparent discrepancies as to the rate of discharge in 

 the results obtained by different observers, and by different methods, 

 far from exciting distrust of them all, really lend support to the idea 

 of a fundamental and fairly constant rhythm in the outflow as soon 

 as it is recognized that the higher rates are approximately multiples 

 of the lower. Thus, the number deduced by Helmholtz from the ex- 

 periment of the springs is twice the lowest rate calculated from graphic 

 records of the contraction. The rates corresponding to the muscle- 

 sound and to the frequency of the electrical oscillations are about four 

 times this number. Now, in a vibrating elastic body like a contracting 

 muscle, a simple mathematical relation of this sort might be expected 

 to appear when determinations of the rate of oscillation and of accom- 

 panying periodic changes are made by methods varying in principle and 

 in delicacy. For instance, an arrangement suited to record and to 

 count coarse vibrations could not be expected to give the same result 

 as an arrangement suited to record and count fine vibrations. But if 

 both the coarse and the fine vibrations were related to a fundamental 

 rhythm, a simple proportion might be expected to exist between the 

 two sets of results. 



(3) Thermal Phenomena and Transformation of Energy in the 

 Muscular Contraction. When a muscle contracts, its temperature 

 rises; the production of heat in it is increased. This is most dis- 

 tinct when the muscle is tetanized, but has also been proved for 

 single contractions. The change of temperature can be detected 

 by a delicate mercury or air thermometer; and, indeed, a ther- 

 mometer thrust among the thigh-muscles of a dog may rise as much 



