MUSCULAR AND SKELETAL SYSTEMS. 23 1 



in swimming, and against the air in flying. For instance, 

 let a steam engine be lifted from the rails and steam be 

 put on ; we have only wheel motion. But while thus 

 working set the engine on the track, and wheel motion 

 is changed into locomotion. Or lift a cyclist above the 

 ground and let him work his pedals ; we have now 

 limb motion and wheel motion. But set him on the 

 ground, and away he shoots, scorching the ground as he 

 passes; wheel motion is converted into locomotion. Or, 

 again, take the sprinter, hang him up in the air, and let 

 him set his running muscles into action. We have, of 

 course, only extravagant limb motion. But while this 

 is going on, if we set him down on the earth, instantly 

 limb motion is converted into rapid locomotion. There 

 is therefore no new principle involved, and no further 

 discussion required. 



But there is still one point which must be mentioned 

 — viz., the exquisite co-ordination of action of many mus- 

 cles required in nearly all our motions. For example, 

 in the. simple act of standing there are probably at least 

 one hundred muscles in perfect co-ordinate action to 

 maintain the equilibrium. It is so easy and so instinct- 

 ive that we are unconscious of the constant play of 

 many muscles. If so in standing, how much more in 

 walking, running, leaping, swimming, flying! So won- 

 derful, indeed, is this co-ordination that it could not be 

 learned in a lifetime if it were not largely inherited. A 

 calf newly born will stand on its feet and walk. It has 

 not learned to do so, but has inherited the capacity. A 

 chick newly hatched will walk and use its eyes correctly 

 and peck its food. A wild bird's egg may be taken 

 from the nest, hatched in an incubator, and reared in a 

 cage until the young bird is well feathered, until nerves 

 and muscles are sufficiently developed. If then it be 

 carried out and thrown in the air it will at once fly away 



