processes, brought about by means of the memory of the nervous
system, enter but partly within the domain of consciousness,
remaining unperceived in other and not less important respects. This
is also confirmed by numerous facts in the life of that part of the
nervous system which ministers almost exclusively to our unconscious
life processes. For the memory of the so-called sympathetic
ganglionic system is no less rich than that of the brain and spinal
marrow, and a great part of the medical art consists in making wise
use of the assistance thus afforded us.

To bring, however, this part of my observations to a close, I will
take leave of the nervous system, and glance hurriedly at other
phases of organised matter, where we meet with the same powers of
reproduction, but in simpler guise.

Daily experience teaches us that a muscle becomes the stronger the
more we use it. The muscular fibre, which in the first instance may
have answered but feebly to the stimulus conducted to it by the motor
nerve, does so with the greater energy the more often it is
stimulated, provided, of course, that reasonable times are allowed
for repose. After each individual action it becomes more capable,
more disposed towards the same kind of work, and has a greater
aptitude for repetition of the same organic processes. It gains also
in weight, for it assimilates more matter than when constantly at
rest. We have here, in its simplest form, and in a phase which comes
home most closely to the comprehension of the physicist, the same
power of reproduction which we encountered when we were dealing with
nerve substance, but under such far more complicated conditions. And
what is known thus certainly from muscle substance holds good with
greater or less plainness for all our organs. More especially may we