68 



PHYSIOLOGY OF MUSCLES AND NERVES. 



and that the force — the tension exercised bj the muscles 

 of the calf — acts obliquely on the lever. It is of course 

 impossible to determine the diameter in a living man ; 

 it must be observed in a dead body of about the same 

 size as that of the person experimented on. 



Henke also has lately determined the value of the 

 absolute force of human muscle. He used the flexor 

 muscles of the forearm (cf. fig. 23) to determine this. 

 In the figure, a represents the upper arm, b the fore- 

 arm — the former being in a ver- 

 tical, the latter in a horizontal 

 position ; c represents the muscles 

 which raise or bend the forearm. 

 (There are in reality two of these 

 muscles, 31, biceps and M, bra- 

 chialis internus). Supposing that 

 the muscles are stretched, and 

 weights are placed on the hand 

 till the muscles are no longer ca- 

 FiG. 28, DiAGHAM OF THK pable of raislug the hand, then, 



FLEXOU MISCLES OF THE : x „ • j.1 • j 'i.! 



FOREAUM. .1^^^^ ^^ ^^^ ^'^^ experiments with 



the muscles of frogs, equipoise is 

 obtained between the tendency of the muscle to con- 

 tract and the weight carried. Care must, however, be 

 taken that the muscles act on a long lever arm, the 

 weight on a short one, and the weight of the forearm 

 itself must also be taken into consideration. Due at- 

 tention being given to all these circumstances, and to 

 the diameter of the muscles when drawn into action, 

 Henke calculated that the absolute force in human 

 muscle is equal to from six to eight kilogrammes. Ex- 

 perimenting in a similar way on the feet, he found 

 somewhat lower figures in that case. Weber, however. 



