n
suggested that the conversion under tetanisation of modified response to
normal, in stale nerve, is due to a hypothetical evolution of CO_2 in
the nerve during stimulation.[16]

#(2) In metals.#--I have, however, met with exactly parallel phenomena in
metals, where, owing to some molecular modification, the responses
became reversed, and where, under continuous stimulation, though here
there could be no possibility of the evolution of CO_2, they tended
again to become normal.

If after mounting a wire in a cell filled with water, it be set aside
for too long a time, I have sometimes noticed that it undergoes a
certain modification, owing to which its response ceases to be normal
and becomes reversed in sign. I have obtained this effect with various
metals, for instance lead and tin, and even with the chemically inactive
substance--platinum.

[Illustration: FIG. 75.--ABNORMAL POSITIVE (UP) RESPONSE IN NERVE
CONVERTED INTO NORMAL (DOWN) RESPONSE AFTER CONTINUOUS STIMULATION T
(WALLER)
The galvanometer is not dead-beat, and shows after-oscillation.]

The subject will be made clearer if we first follow in detail the
phenomenon exhibited by modified nerve, giving this abnormal response.
The normal responses in nerve are usually represented by 'down' and the
reversed abnormal responses by 'up' curves. In the modified nerve, then,
the abnormal responses are 'up' instead of the normal 'down.' The record
of such abnormal response in the modified nerve is shown in fig. 75. It
will be noticed that in this, the successive responses are undergoing a
diminution, or tending towards the normal. After continuous stimulation
or tetanisation (T), it will be seen that the abnormal or 'up' responses
are converted into normal or 'down.'

I shall now give a record which will exhibit an exactly similar
transformation from the abnormal to normal response after continuous
stimulation. Here the normal responses are represented by 'up' and the
abnormal by 'down' curves. This record was given by a tin wire, which
had been molecularly modified (fig. 76). We have at first the abnormal
responses; successive responses are undergoing a diminution or tending
towards the normal; after continuous stimulation (T), the subsequent
responses are seen to have become normal. Another record, obtained with
platinum, shows the same phenomenon (fig. 77).

[Illustration: FIG. 76 AND FIG. 77
Abnormal 'down' response in tin (fig. 76) and in platinum (