Response in the Living and Non-Living

Conditions for obtaining electric response-Method of injury -Current of injury-Injured end, cuproid: uninjured, zincoid-Current of response in nerve from more excited to less excited-Difficulties of present nomenclature-Electric recorder-T wo types of response, positive and negative -Universal applicability of electric mode of response-Electric response a measure of physiological activity-Electric response in plants.UNLIKE muscle, a length of nerve, when mechanically or electrically excited, does not undergo any visible change.That it is thrown into an excitatory state, and that it conducts the excitatory disturbance, is shown however by the contraction produced in an attached piece of muscle, which serves as an indicator.But the excitatory effect produced in the nerve by stimulus can also be detected by an electrical method.If an isolated piece of nerve be taken and two contacts be made on its surface by means of non-polarisable electrodes at A and B, connection being made with a galvanometer, no current will be observed, as both A and B are in the same physico-chemical condition.The two points, that is to say, are iso-electric.If now the nerve be excited by stimulus, similar disturbances will be evoked at both A and B. If, further, these disturbances, reaching A and B almost simultaneously, cause any electrical change, then, 8 RESPONSE IN THE LIVING AND NON-LIVING through the non-polarisable electrode is from left to right.The uninjured end is therefore comparable to the zinc in a voltaic cell (is zincoid), the injured being copper-like or cuproid.! If the electrical condition of, say, zinc in the voltaic couple (fig.8, c) undergo any change (and I shall show later that this can be caused by molecular disturbance), then the existing difference of potential between A and B will also undergo variation.If for example the electrical condition of A approach that of B, the potential difference will undergo a Fic.3.-DIAGRAM SHOWING THE CORRESPONDENCE BETWEEN INJURED (B) AND UNINJURED (A) conTacts IN NERVE, AnD Cu anp Zn 1n A Vottaic ELEMENT Comparison of (c) and (d) will show that the injured end of B in (d) corresponds with the Cu in (c).diminution, and the current hitherto flowing in the circuit will, as a consequence, display a diminution, or negative variation.Action current-We have seen that a current of injury-sometimes known as 'current of rest -flows in a nerve from the injured to the uninjured, and that the injured B is then less excitable than the uninjured A. If now the nerve be excited, there being a greater 1 In some physiological text-books much wrong inference has been made, based on the supposition that the injured end is zinc-like.