Page:Life in Motion.djvu/132

112 the nature of the apparatus at the end of the wire. Here is a wire conducting a powerful current. At this point, we cause it to branch out so as to divide the current into a number of streams. You see here the current decomposing water, there magnetising soft iron, here again doing the mechanical work of turning a wheel. In like manner, there is contraction of a muscle if the nerve ends in a muscle, change in the calibre of a blood-vessel if the nerve ends in that structure, secretion from a gland if the nerve is connected either with the vessels or the cells of a gland, an electric discharge or shock if the nerve terminates in the electric organ of an electric fish, and a feeling or sensation if the nerve-fibre goes to a sentient brain.

But if nerves are of so much importance, you will naturally ask how motions are produced in animals that have no nerves. Many animals show not a trace of nervous structures and yet they move. Again, the hearts of some animals beat with great regularity and still no nerve-fibres exist in their tissue. Such nerveless structures respond to a stimulus. Give them a shock of electricity and they