Page:Life in Motion.djvu/123

Rh it shows nothing. The electric shocks sent to it produce no evident result. We must not assume, however, because we see nothing following the irritation of a nerve, that nothing happens. There may be changes in the nerve for all we know to the contrary, and the fact that changes do occur in the nerve would be evident if the nerve had still been connected with a muscle, because then, as you now know, irritation of the nerve would have been followed by contraction of the muscle. We would have seen the muscle move, and that would have been a proof that something really occurred in the nerve at the point of irritation, and that something passed along the nerve to the muscle. But perhaps you think I am going a little too fast. You may say that it is possible that irritation of the nerve at one point causes an instantaneous change throughout all the nerve, and that nothing really passes along it. Now this is a question that we can only settle by experiment.

Suppose that we irritate a nerve close to where it enters a muscle, the muscle will not contract at the instant the stimulus is applied to the nerve. There is always a loss of time.