410 WORK OF THE PHYSIOLOGICAL STATION AT PARIS. 



Guided by certain theories it occurred to me tbat tbc muscular sys- 

 tem uiiylit also be modified and the form of a muscle changed by 

 altering- the range of its movements. The result, as we shall see, has 

 confirmed my anticipations. 



Let us take up again the well-marked example of the unequal length 

 of the gastrocnemii muscles in the white man and in the negro. If the 

 white man, as we have said, has the shorter calf, it is on account of 

 the shortness of his calcaneuni. Suppose that the length of the calca- 

 neum in an animal is diminished. If the muscle adapts itself to the 

 new conditions of work it ought to diminish in length. 



The rabbit is well adapted for such an experiment. It has a very 

 long calcaneum, and consequently the extensor nuiscles (»f the foot 

 have very long, red fibers. 1 resected in a rabbit a third of the length 

 of the calcaneuni, and placed the limb operated uj^on in a x)laster cast 

 until the bone was entirely united. The animal was then set free in a 

 large yard, where soon it was running about with as much agility 

 as its companions. At the end of a year the rabbit was killed and it 

 was seen that upon the side operated upon the muscles had become 

 modified in accordance with the theory. The red fibers were redu(;ed 

 to about a third of their length and replaced by tendon. A com- 

 j)arison of the sound limb with that operated upon showed this change 

 in a striking manner. 



I made an experiment which was the converse of this by an oiier- 

 ation upon a kid. In this species only the ungual extremity of the foot 

 strikes the ground, and the calcaneum, always raised, moves but slightly 

 in walking. The resection of this bone had, therefore, but little 

 effect either upon the mode of locomotion of the animal or upon the 

 character of its muscles. 



Finally IM. W. Roux has given numerous examples of the modifica- 

 tions of the muscles of man after partial anchyloses which reduced, 

 more or less, the range of movements. He has shown in a great num- 

 ber of autopsies a diminution in tlie length of the red fibers and their 

 replacement by tendon. This diminution in length was always proj)or- 

 tional to the reduction which had occurred in the range of movement. 



The adaptations of muscles to mechanical conditions experimentally 

 created by nuitilations is then well established. It is more than prob- 

 able that similar adaptations may be obtained in the length of the 

 muscles of animals by jjlacing them in conditions where they would be 

 forced to make movements more extensive than those of their normal 

 life, by obliging them, for examjjle, to leap or climb to get their food. 

 I will shortly cite some facts of this kind. 



But even if it is shown that in an individual the muscles and the 

 skeleton become adapted to conditions of work, this would not be sutti- 

 cient to explain transformism. It is, in fact, necessary, in order to cause 

 a variation of species, that the modification aciiuired by individuals 

 should be transmitted to their descendants by heredity. 



