STRIATED MUSCLE. 87 



muscles, or on the number of fibres of which they are com- 

 posed. Rosenthal discovered, in experimenting on the 

 muscles of a frog,, that the contracting force of the adduc- 

 tor muscles in the thigh of this animal varies (in the whole 

 transverse section, that is, one square centimetre) from two 

 to three kilogrammes. In the gastrocnemii and soleus in 

 man it is about eight kilogrammes to a square centimetre. 

 This experiment is easily made on man. The person to be 

 experimented upon stands upright, and such a weight is 

 placed upon his body as to render it quite impossible for him 

 to rise upon his toes or raise his heels from the ground. At 

 this moment the weight of the body, with the weight added 

 to it, plainly represents the force, or weight necessary to 

 neutralize the movement which the muscles of the calf have 

 a tendency to produce when the person rises upon the toes, 

 or, better still, on the extremities of the metatarsals. The 

 exact force of the muscles of the calf is thus equal to the 

 value of this weight divided by the length of the lever arm 

 (see farther on, mechanism of the skeletort: lever of the 

 second kind) ; given, then, the mean transverse section of 

 the muscular mass of the calf (gastrocnemii and soleus), it is 

 easy to deduce from it the exact force of the whole surface 

 of these muscles. 



The total weight of the mass of the muscles in man 

 shows that, in a mechanical point of view, these organs form 

 machines quite powerful and perfect ; and that, in proportion 

 to their weight, which is comparatively very light, they 

 develop a much greater force than any machine that we can 

 construct. 1 



Physiologists have analyzed still more closely the phenom- 

 enon presented by the passage from the first to the second 

 form, and have sought to discover the molecular modifica- 

 tions which take place in the muscular fibre during this phe- 

 nomenon. 



It is scarcely worth while to mention the theory which 

 explained the second form as being a zigzag folding of the 

 muscular fibre (Prevost and Dumas, 1823), this theory hav- 

 ing been proved to be founded on an error in observation. 

 In this case the muscular fibre, being placed upon a sheet of 

 glass, adhered to it by its sheath, so that, after taking the 

 second form, it could not easily return to the first, its 

 adherences causing it to bend in a broken line ; it is then 



1 Weber, Rosenthal, Hermann. 



