396 



THE PROPERTIES OF STRIPED MUSCLE. 



A bit of E string 2 in. long is so arranged that its shortening may be recorded 

 myographically (Fig. 219). It is extended by a load of 50 grms. and surrounded 

 by a coil of thin platinum wire iu connection with the two poles of a fairly 

 strong battery, so that it can be promptly heated or brought back again to the 

 temperature of the water in which it is immersed, by closing or opening the 

 current which flows through the wire. Before making the experiment, the 

 water is warmed gradually to a temperature above that at which the experi- 

 ment is to be made, namely, to about 50° C, in consequence of which the string 

 is permanently shortened to a certain length. Under these conditions 

 momentary closure of the current is followed by a rapid rise of the writing- 

 lever, which describes a curve resembling a myogram. 



By soaking and heat- 

 ing the cord before the 

 experiment, it has been 

 made to assume a constant 

 condition, i.e., one in 

 which the observation can 

 be repeated any number 

 of times. We have there- 

 fore before us a process 

 in which Avork, compar- 

 able to that of muscular 

 contraction, is done by a 

 " cyclical " process at the 

 expense of heat ; a tension 

 of 300 grms. being, for 

 example, developed in a 



string 



30 mm. long and 



only 1 square mm. in 

 transverse section, by 

 raising the temperature 

 75° C. 1 If the same ex- 

 periment be made with 

 stretched indiarubber in- 

 stead of violin string, the 

 effect is even greater ; if 

 heated by only about 

 20° C. it shortens in the 

 direction in which it has 

 been extended, and can 

 be made thereby to do an 

 amount of work "sixty 

 times as great as the 

 maximum afforded by 

 human muscles of the same transverse sections." 2 



The three substances — catgut, stretched caoutchouc, and muscle — all 

 resemble one another in being doubly refractive or containing doubly refractive 

 elements. The property of contracting when heated is one which, according 

 to Engehnann, is met with in doubly refractive bodies, and varies with the 

 degree in which they are so. 3 It is for this reason that stretched indiarubber, 

 which is made up entirely of doubly refractive substance, can do more work 

 than either a muscle or catgut string when similarly heated. A further resem- 

 blance that he finds between muscle and other such substances is, that within 



1 Engehnann, "Sur l'origine de la force musculaire," Arch, neerl. d. sc. exactes, vol. xxvii. 

 p. 24. See also Engehnann, "Ueber einige gegen meine Ansicht voni Ursprung der 

 Muskelkraft erhobene Bedenken," Arch. f. d. gcs. Physiol., Bonn, Bd. liv. S. 637. 



2 Croonian Lecture, p. 426. 3 Ibid., p. 419. 



Fig. 219. — Engelmann's apparatus for recording contractions 

 of a violin string on heating, b a, support, to the one 

 end of which (a) the previously swollen violin string is 

 attached. H, writing-lever, supported at c, to which 

 the other end of the string is attached, d and d' , 

 weights for altering tension. + and - , the two ends 

 of the platinum wire coiled round the string leading 

 to the two poles of a battery, th, thermometer with 

 its bulb in the same bath in which the string is 

 immersed. 



