GENEKAL PHYSIOLOGY OF MUSCLE 



47 



the volume or mass of the muscle. These relations between the 

 size of a muscle and the energy it is capable of developing : 



between the length of a muscle consisting of parallel fibres and its 

 degree of contraction ; and finally between the weight of the 

 muscle and the useful work it is capable of yielding were all 

 noted by Borelli in the early half of the eighteenth century, and 

 were fully considered and cleared up by Weber in 1845. 



The absolute force of a muscle is measured by the minimal 

 weight that it is unable to lift under maximal excitation (Weber). 

 Since it is proportional to the cross-section or diameter of the 

 muscle, a universal standard is obtained by calculating the absolute 

 force of a square centimetre of the muscle section. The absolute 

 force of the muscles varies in 

 different animals and even in 

 different muscles of the same 

 animal. It varies for a square 

 cm. of frog's muscle between 7 

 and 8 kgrms. (Henke and Knorz) 

 or even 9 and 10 k grins. (Koster, 

 Haughton). 



Attempts have also been made 

 to determine the absolute force 

 of a sq. cm. of human muscle by 

 measuring the cross -section on 

 a dead subject of the same 

 physique and muscular develop- 

 ment as the subject of experi- 

 ment. Here, again, the values 

 obtained were very different : 

 2-8-3 kgrms. (Eosenthal), 5-10 

 kgrms. (other experimenters). It 

 should be noted, however, that these experiments on man were made 

 not with artificial tetanisation, but with a voluntary yield of work, 

 in which the energy developed may be double, or at least a third 

 more than that developed on stimulation with a tetanising current. 



From the clinical point of view, investigation of the relative 

 strength of certain groups of human muscles is far more practicable. 

 The dynamometer is usually employed for this purpose. It consists 

 of a strong oval steel spring, which is compressed by the hand, while 

 an index moves along an empirically graduated scale to indicate 

 the amount of compression and thus of the power developed in the 

 group of muscles which come into play when the hand is closed. 



The figures obtained by this instrument are, however, of little 

 value, since they can be modified by practice, attention on the part 

 of the subject, and, above all, degree of voluntary effort, which may 

 vary considerably, even independently of the conscious will of the 

 subject. 



FIG. 27. Dynamograph. (A. D. Waller.) 



