WALKING. 



traction of the muscle, are drawn closely and firmly 

 around the object which they embrace. Is it not so ? 



Dr. B. Yes ; and observe too, that the greater the 

 weight of the body by which the muscle is bent, the stron- 

 ger will be the grasp. In this way they are enabled to 

 grasp a branch so firmly, as to sleep secure, even when 

 agitated by the winds. 



Emily. I have often wondered how birds could roost 

 without being liable at every moment to lose their bal- 

 ance, and tumble off in their sleep. But how simply 

 though perfectly is this accident obviated, by this sin- 

 gular arrangement. Still, some muscular exertion is 

 necessary to prevent the body from pitching forward 

 or backward, and I do not see how this ca*n take place 

 while the animal is sleeping. 



Dr. B. A certain degree of muscular strength in- 

 deed, they do exert ; and it is so even with ourselves. 

 When we lie down to sleep, the limbs must either be 

 perfectly straight, which will require the action of the 

 extensors, or bent, requiring the action of the flexors > 

 so that whatever position we take, some muscles must be 

 put into action. Birds are endowed with the power of 

 making greater muscular exertion during sleep, and con- 

 tinuing it for a greater length of time, than man. 



The most common kind of progression used by man. 

 is that of walking, and though every body of sound limb 

 is capable of performing this process, very few indeed 

 are aware of the complicated, yet harmonious series of 

 motions necessary to be executed before a single step 

 can be completed. 



Emily. I can vouch for not making one of that few, 

 for it w r ould as soon have entered my head to ask how 

 I eat or sleep, as how I walk. But I am no less de- 

 sirous of being informed precisely how this process is 

 accomplished. 



Dr. B. Suppose now a person to be standing firm 

 and erect on both feet, ready to take the first step. His 

 first motion is to throw the weight of the body on on** 



