144 THE WORK DONE. [BOOK L 



with the height of the contraction, that is with the amount of 

 shortening, but with the work done. And this is measured by 

 multiplying the number of units of height to which the load is 

 raised into the number of units of weight of the load. Hence 

 it is obvious from the foregoing observations that the work done 

 must be largely dependent on the weight itself. Thus there is 

 a certain weight of load with which in any given muscle, stimu- 

 lated by a given stimulus, the most work will be done ; as may be 

 seen from the following example : 



Load, in grammes 50 100 150 200 250 



Height of contractions in millimeters 14 9 7 5 2 

 Work done, in gram-millimeters ... 450 700 750 400 



82. The Influence of the Size and Form of the Muscle. Since 

 all known muscular fibres are much shorter than the wave-length 

 of a contraction, it is obvious that the longer the fibre, the greater 

 will be the shortening caused by the same contraction wave, 

 the greater will be the height of the contraction with the same 

 stimulus. Hence in a muscle of parallel fibres, the height to 

 which the load is raised as the result of a given stimulus applied 

 to its nerve, will depend on the length of the fibres, while 

 the maximum weight of load capable of being lifted will depend 

 on the number of the fibres, since the load is distributed among 

 them. Of two muscles therefore of equal length (and of the same 

 quality) the most work will be done by that which has the larger 

 number of fibres, that is to say, the fibres being of equal width, 

 which has the greater sectional area; and of two muscles with 

 equal sectional areas, the most work will be done by that which 

 is the longer. If the two muscles are unequal both in length 

 and sectional area, the work done will 1 be the greater in the 

 one which has the larger bulk, which contains the greater number 

 of cubic units. In speaking therefore of the work which can be 

 done by a muscle, we may use as a standard a cubic unit of bulk, 

 or, the specific gravity of the muscle being the same, a unit of 

 weight. 



We learn then from the foregoing paragraphs that the work 

 done, by a muscle-nerve preparation, will depend, not only on the 

 activity of the nerve and muscle as determined by their own 

 irritability, but also on the character and mode of application 

 of the stimulus, on the kind of contraction (whether a single 

 spasm, or a slowly repeated tetanus or a rapidly repeated tetanus) 

 on the load itself, and on the size and form of the muscle. Taking 

 the most favourable circumstances, viz. a well-nourished, lively 

 preparation, a maximum stimulus causing a rapid tetanus and an 

 appropriate load, we may determine the maximum work done by a 

 given weight of muscle, say one gramme. This in the case of the 

 muscles of the frog has been estimated at about four gram-meters 

 for one gramme of muscle. 



