218 THE PHYSIOLOGY OF MUSCULAR WORK 



respectively ; there are also present maltase and an oxidising 

 ferment, or oxydase. These ferments doubtless play important 

 parts in the exchange of material in the muscle, for in addition to 

 their definite action there is the probability of a reversible action ; 

 the breaking down process may, according to the condition of 

 the tissue, be replaced by the building up or synthetic process. 



CHAPTER II 



FACTS concerning the structure, and the physical, chemical, and 

 physiological properties of muscle, have been given as an intro- 

 duction to the physiology of muscular work. It is now necessary 

 to study the effects of muscular exercise or work upon the living 

 organism, especially man. 



The origin of muscular activity we cannot trace, nor can we 

 think of its beginning in the offspring of any animal. Muscular 

 activity is a specialised form of protoplasmic movement, and the 

 capacity for such movement is an attribute of the minute male 

 and female cells from the union of which the offspring arises. 

 There has been a continuity of life from parent to offspring through 

 countless generations, and this carries with it the potentiality of 

 muscular movement. Heredity has a far-reaching influence upon 

 muscular development and activity ; even at birth the power of 

 co-ordination possessed by some animals is remarkable. A guinea- 

 pig is born with its eyes opeji and its body covered with fur, and it 

 is able to run about ; a calf within a few minutes of first seeing the 

 light is able to walk and seeks its mother's teats. These young 

 animals do not learn to walk, but learn by practice to make perfect 

 the power of walking which they possess at birth. A marked 

 contrast is seen in the newly born rabbit, rat, and mouse ; they 

 are blind, naked, and helpless. A study of birds reveals a similar 

 difference. Within an hour or two of hatching the chick is able 

 to run about and peck up its food ; the pigeon, on the other hand, 

 is for several days blind, naked, and helpless. The maturity or 

 immaturity of different classes of animals at birth is related to the 

 natural habits of the race and to adaptation. 



The condition of the newly born child is intermediate between 

 the extreme examples just given ; its muscular development and 

 power of co-ordination are considerable, and are especially seen 



