VARIABILITY OP THE MUSCULAR SYSTEM. 95 



and regulates it according to the laws which we must now 

 endeavour to make known. 



Nothing in the organic form is under the dominion of 

 chance. The specific varieties of living beings have been too 

 often compared to the fancies of an architect, who, while 

 adhering to an uniform plan, invents a thousand varieties of 

 details, as a musician composes a series of variations on a 

 given theme. 



In our present inquiry we may say that the great variety 

 which is found in the muscular apparatus, whether in the 

 different parts of the body of an animal^, or in the homologous 

 parts of animals of different species; for instance, varieties 

 in the volume or the length of muscles; the very unequal 

 partition of the red contractile fibre, and the inert, white, 

 glistening fibre of the tendon ; that all this is entirely subject 

 to the dynamic laws of muscular function. 



Adaptation of the form of muscles to the requirements of function. 

 Normal anatomy can only furnish us with examples of the 

 harmony which exists between the form of the organs and 

 their habitual function. Experiment alone can show us that, 

 by changing the function, we may bring into the form of the 

 organs modifications which may harmonize them with the 

 new conditions which may be imposed upon them. It will 

 be easy to make experiments for this purpose. From the 

 moment when we know in what direction the modification 

 ought to be produced, in order to adapt the organ to the 

 function, the changes effected in animals placed by us under 

 conditions of peculiar muscular function, will derive an im- 

 portant significance. But while we wait for the realization of 

 this vast series of experiments, there are some which we can 

 employ even now. Experiments made ready to our hand are 

 furnished by pathological anatomy. 



Medicine and surgery are full of information on this in- 

 teresting subject. They show us, for example, that it is 

 movement itself which keeps up the existence of the muscle. 

 A long repose of this organ brings about first the diminution 

 of its volume, and soon a change in the elements which com- 

 pose it. Fatty corpuscles are substituted for the striated fibre 

 which form its normal element; at last, these corpuscles, 



