356 



THE PROPERTIES OF STRIPED MUSCLE. 



larger than in either of the two other cases ; but during the succeeding 

 part nothing further will be accomplished. There would, however, 

 be no such fruitless period if the load were diminished throughout 

 at the same rate as the length of the muscle; for in that case the 

 muscle would at every moment have as much work as it could manage. 



Acting on this principle, Tick has contrived an instrument (Fig. 190) 

 which may be called a cosine lever. When this is interposed between 

 the muscle and the weight it has to lift, the former is enabled to work 

 under conditions which approximate to those required. 



It consists of two bars which can be screwed together at any angle. They 

 rotate on the axle C. From the left upper arm a weight can be hung 

 at any distance from C. On the right upper arm at M, the muscle acts. 

 The rotation of the lever is checked at A and A'. The cross must be so 

 arranged that, during the period of shortening of the muscle, the rotatory 

 moment of the weight shall diminish from a maximum that of the initial 

 tension to zero; and CM must be of such length that the muscle in con- 

 tracting with a minimal load shall rotate the bar M 60, in which case the 

 distance through which M descends must be equal to CM. For this purpose, 

 it is convenient that the levers should be set at an angle of 60 to each other. 



The mode of experimenting is as follows: After being tetanised, the 

 muscle is allowed to shorten, and in so doing to act on the shorter end of the 

 lever H H ', the long arm being attached by a long cord to the cosine lever 

 at M. In an experiment, of which the data are given by Fick, a weight of 

 200 grins. , L, was attached to the lever at 90 mm. distance from C, while 

 the muscle, which had been previously found to shorten from 50 to 24 mm., 

 acted on the other lever at 52 mm. distance from the same axis. Obviously, 

 the rotatory moment of L on the axis C is proportional to the cosine of the 

 angle of inclination of the bar L C. The completely tetanised muscle had been 

 found to exercise at d an initial traction of 800 grins., consequently at M of 

 400 grms., for AH' is twice as long as A d. Its rotatory moment was therefore 

 52 x 400 x cos 30 = 20,800 cos 30. As the rotation of C produced by the 

 contraction of the muscle amounted to 60, M was pulled down 52 mm., and 

 L raised 45 mm., so that the amount of work done was 9000 grm. mm. 1 



The amount of work which, according to calculation, would have been 

 required to stretch the same excited muscle from its natural or equilibrium 

 length in tetanus, to its equilibrium length when at rest, was 9200 grm. mm., 

 an amount which so nearly corresponds with that of the external work it was 

 found to be able to do, as to afford no sufficient reason for doubting that, under 

 the conditions in question, the whole of the available mechanical energy of 

 the muscle was brought into play. By a slight increase of the distance L C, 

 the correspondence might have been made closer. 



Other experiments show that it is not possible to make a muscle do 

 the amount of external work which corresponds to the negative work 

 done on it in extending it from its excited to its unexcited length, 

 except under such conditions as have been stated, and that the more 

 nearly these are approached the larger is the proportion of work 

 actually done to what theoretically might be done. The muscle acts 

 advantageously, because, during the whole period of its action, the work 

 it is called upon to do is always as much as it can master, and 

 diminishes as it becomes less fit for it ; or, to use the language in which 



1 From 30 to the cosines decrease nearly at the same rate as the angles. Between 

 60 and 30 they obviously decrease more slowly. This, however, does not appear to 

 interfere with the result. It is possible to give a simpler form to the cosine lever, I 

 prefer, however, not to modify Fick's figure. 



