404 



THE PROPERTIES OF STRIPED MUSCLE. 



which moment it no longer has any load to lift. If the same muscle is 

 tetanised for the same period, sustaining a weight which, at first 

 approximately 0, is gradually increased to the amount of the initial 

 weight in the previous case, it will then (after first promptly shortening 

 in response to the excitation) be stretched to the length which it had 

 before, when charged as it is now with a load it was only just able to 

 lift. 



In the two cases the excitation is the same ; the contrast between them 

 consists in the mechanical conditions under which the muscle responds. 

 In the first case it does its utmost amount of work ; in the second case it 

 not only does no work, but is worked upon by the descending weight which 

 stretches it. In both, the temperature of the muscle is raised, but in 

 the former this represents only a part of the chemical change (oxida- 

 tion) which takes place ; the remainder becomes external in work. In 

 the latter the warming of the muscular substance represents more than 

 the heat production due to oxidation, for a considerable part of it is due 

 to the action of an external cause, the extension of the muscle by the 

 weight. 



The results of 

 the experimental 

 comparison of the 

 two cases have been 

 given by Fick in one 

 of his recent re- 

 searches. 1 The 

 method will be 

 readily understood 

 with the aid of the 

 diagram (Fig. 220), 

 which represents 

 Blix's ingenious con- 

 trivance for obtain- 

 ing the extension 



curve of a muscle. The slider SS can be freely moved backwards and 

 forwards on the rails R JR', K K', between which it works. At one end 

 of it there is a support A, from which the muscle is suspended. The 

 other end of the muscle is attached to the myographic lever at b. The 

 axle a on which this lever rotates is carried by the slider. The load 

 is sustained by a vertical rod /, which rests on the lever at r, and moves 

 freely up and down between the pins t t and 1 1' ; consequently the dis- 

 tance between the point at which the load is sustained by the lever, and 

 the axle a varies according to the position of S S. The plate on which the 

 lever writes is fixed. The curved lines inscribed on it are such as would be 

 drawn by an up-and-down movement of }j, if the index of the slider were 

 brought in succession to the points 1, 2, 3, etc., on the scale and back again. 

 It will be seen at once that if the muscle is unexcited, p will describe its exten- 

 sion curve on the plate, whenever the slider is moved along its whole course in 

 either direction. If the load is 1000 grms., and the maximum distance 

 between r and a one-half of the distance between a and b> each division of 

 the scale (i.e. one-tenth of this distance) will correspond to 50 grms. of tension. If 

 during the time (say 2 seconds) that the slider accomplishes its backward and 

 forward journeys, the muscle is tetanised, it draws in like manner the extension 

 curve of tetanised muscle. If contracted muscular fibre were to behave in 



1 Fick. "Neue Beitrage zur Kenntniss von der Warmeentvvickelung im Muskel," Arch, 

 f. d. ges. Physiol, Bonn, 1892, Bd. li. S. 541. 



FIG. 220. Blix's apparatus for taking the extension curves of 

 muscle with the load either increasing or decreasing. 

 After Fick. 



