Page:Life in Motion.djvu/192

172 is due to the death or dying of the layer of muscle-substance laid bare by the transverse section. Dying muscle-substance, it would appear, becomes negative to living substance. But the negative variation current, or the action current, as we may well term it, indicates changes happening in the muscle, changes that are somehow connected with the phenomena of contraction. It may be detected by special methods without even injuring the muscle.

It was supposed, until recently, that the negative variation occurred solely in the period of latent stimulation, a period perhaps as short as the one-two-hundredth of a second; but by special photographic methods of exquisite delicacy, Professor Burdon Sanderson has shown that this is not the case, and that it continues into the time of the contraction of the muscle. Nor have we any definite proof that these electrical changes are dependent on the chemical changes discussed in last lecture, although it is highly probable that the two are intimately connected.

May not the negative variation change in one set of muscular fibres do something in