Inhibition and the action of drugs on inhibitory centres play a very important part indeed in pharmacology, and on the present hypothesis they are very puzzling.

By inhibition we mean the power of restraining action which some parts of the nervous centres possess. At present it is usually. supposed that certain parts of the nerve-centres, instead of having a sensory or motor function, have an inhibitory one peculiar to themselves. It is found, however, that inhibitory powers are not confined to Setschenow's centres, already mentioned (p. 166), but that almost any part of the nervous system may have an inhibitory action on other parts, so that it becomes almost necessary to abandon the old hypothesis. It is found, for example, that not only is reflex action more active in the frog when the optic lobes are removed, but that when the spinal cord is taken away in successive slices from above downwards, the reflex action in the part below goes on increasing. On the old hypothesis we are almost obliged to assume that each nerve-cell has, two others connected with it, one of which has the function of increasing or stimulating, and the other of inhibiting its action. Most of the phenomena which we find can be explained in a much simpler way by supposing that nervous stimuli consist of vibrations in the nerve-fibres or nerve-cells, just as sound consists of vibrations.

Nature Of Inhibition 96

Fig. 61. - Diagram to show increased intensity of vibration by coincidence of waves.

Fig. 62.   Diagram to show abolition of vibration by interference of waves.

Fig. 62. - Diagram to show abolition of vibration by interference of waves.