n8 THE GROUNDWORK OF SCIENCE

Some, like our respiratory movements, ordinarily take place

independently of our will, but can be performed voluntarily,

and can be voluntarily suspended. Soon, however, the power

of voluntarily restraining them ceases, and they take place in

spite of all our efforts to the contrary. Movements begun

with a voluntary effort may be subsequently carried on

automatically, as we see in setting out for a walk. Such

movements may be carried on much better automatically

than when attended to. Attention often positively impedes

the rapidity and accuracy of our movements, as is easily seen

if we begin to consider what our movements are, as we are

running downstairs.

The agents which induce muscular contraction are termed

stimuli. Such are heat, cold, a puncture, a very acrid or

acid substance, electricity and, normally, the influence of the

nerves supplied to muscles, and emotion and volition each

may be a stimulus. Stimuli physically equal have a more

powerful effect when acting on a muscle through a nerve

than when acting directly on the muscle itself.

We have seen that muscular movements may take place

in us without any advertence thereto on our part, and, of

course, such actions are quite independent of our will. But

much more wonderful, when we come to think over it,

is the fact that muscular contractions will take place in

appropriate groups, resulting in co-ordinated movements

and groups of groups of such movements, which not only

we do not will, but which we do not even know ! How

wonderful, when we carefully consider it, is the trivial act

of a lad throwing a stone at a mark ! How complex must

be the co-ordinated movements between different parts of

the body in order to produce even such a result ! The

lad's mind has little to do with it beyond the one impulse

to hit the mark. He knows nothing of anatomy, but

simply sets going the wonderful mechanism of his body,

Some, like our respiratory movements, ordinarily take place

independently of our will, but can be performed voluntarily,

and can be voluntarily suspended. Soon, however, the power

of voluntarily restraining them ceases, and they take place in

spite of all our efforts to the contrary. Movements begun

with a voluntary effort may be subsequently carried on

automatically, as we see in setting out for a walk. Such

movements may be carried on much better automatically

than when attended to. Attention often positively impedes

the rapidity and accuracy of our movements, as is easily seen

if we begin to consider what our movements are, as we are

running downstairs.

The agents which induce muscular contraction are termed

stimuli. Such are heat, cold, a puncture, a very acrid or

acid substance, electricity and, normally, the influence of the

nerves supplied to muscles, and emotion and volition each

may be a stimulus. Stimuli physically equal have a more

powerful effect when acting on a muscle through a nerve

than when acting directly on the muscle itself.

We have seen that muscular movements may take place

in us without any advertence thereto on our part, and, of

course, such actions are quite independent of our will. But

much more wonderful, when we come to think over it,

is the fact that muscular contractions will take place in

appropriate groups, resulting in co-ordinated movements

and groups of groups of such movements, which not only

we do not will, but which we do not even know ! How

wonderful, when we carefully consider it, is the trivial act

of a lad throwing a stone at a mark ! How complex must

be the co-ordinated movements between different parts of

the body in order to produce even such a result ! The

lad's mind has little to do with it beyond the one impulse

to hit the mark. He knows nothing of anatomy, but

simply sets going the wonderful mechanism of his body,