366 THE PROPERTIES OF STRIPED MUSCLE. 



A tension-writer which has the further advantage of greater simplicity is 

 that of Professor Blix 1 (see Fig. 195 and 195A). The muscle acts by torsion 

 on a cylindrical rod of steel c, 5 mm. long, and nearly 1 mm. thick. This is 

 fixed horizontally at one end ; the other is free, but is supported at s. From 

 a point near the free end a metal bar t' springs, of which the tension-recording 

 arm t is a continuation. At known distances the bar is perforated for the 

 reception of a steel hook, to which the muscle is attached, the usual distance 

 being 3 mm. from the axis. The resistance which the steel rod offers to 

 torsion is such that a weight of 10 to 20 grins, depresses the writing end only 

 1 mm. The arm is 9*6 cms. long, and together with the steel rod weighs 

 only 0*05 grm. The figure shows the way in which the tension-writer is 

 combined with the shortening- writer, so as to register the isometric and 

 isotonic curves synchronically, i.e. the curves occupying corresponding positions 

 on the recording surface of the cylinder. The shortening- writer I is a strip 

 of bamboo, of which the free end is 18 cms. from its axis. It is perforated 

 transversely by a needle about 8 cms. from the axis ; to this needle the lower 

 end of the muscle is attached. This instrument is not only very free from 

 the errors due to inertia and friction, but has the advantage that in employing 

 it for drawing an isometric curve alone, the length of the muscle diminishes 

 extremely little as the tension increases. A tension of 100 grms. can be 

 attained with a diminution of length of no more than 0*06 mm. 



It is desirable for all myographic purposes that the rate of rotation of the 

 recording cylinder should be constant and equable, that the position of the 

 lever at the moment of excitation should be invariable, and that the vibrator 

 which marks the time should start simultaneously with the record. In the 

 instrument designed by Blix all these ends are secured. The rotation of the 

 cylinder is urged by a spring, but is restrained by a detent, on the with- 

 drawal of which the cylinder flies round. In doing so, it liberates a reed 

 which writes its vibrations on the blackened surface, and at a later moment 

 opens the primary circuit of the induction coil. The heavy cylinder, which 

 before this happens has ceased to be acted on by the spring, continues its 

 rotation at a nearly uniform rate, until, after the curves have been drawn, it is 

 arrested by a mechanism which need not be here described. Before the next 

 observation, it must of course be brought back to its original position and 

 adjustment. Although the apparatus above described may admit of further 

 improvement, it answers for the present the requirements of the investigator. 

 It enables him to obtain a true graphic representation of each of the 

 mechanical changes which a muscle undergoes in consequence of excitation by 

 an instantaneous stimulus ; and, by registering tension and length synchronic- 

 ally, to determine both their quantitative relation to each other at any 

 moment, and the relation existing at any moment between their rates of 

 change. 



Experiments in which the mechanical conditions are varied during 

 the response. In v. Kries' first series of experiments relating to this 

 subject, the conditions were such that, although when in the un- 

 excited state the muscle is of its natural length and has no tension, 

 it cannot contract without encountering resistance, which, however, it 

 overcomes as soon as it has gathered sufficient strength. The moment 

 at which this happens is the longer delayed the heavier the weight. 

 In this case the excitatory process begins isometrically and proceeds 

 isotonically. The figure (Fig. 196) shows what happens. 



Curve 1 in both series is drawn by the unloaded muscle, Curves 2, 3, 4, and 

 5 by the same muscle, when loaded successively with increasing weights. All 

 1 Skandin. Arch.f. Physiol., Leipzig, 1892, Bd. iii. S. 295. 



