418 PROCEEDINGS OF SECTION D. 
and Golgi’s impregnation process has furnished brilliant results 
in discovering system and order in that nervous felt-work, the 
grey matter of the central nervous system. The method invented 
by Golgi has further demonstrated that the branches of one cell- 
unit are not continuous with those of another, but that they are in 
apposition. 
Three fundamental facts of nerve physiology have been 
revealed :-— 
(1.) That if a stimulus be applied to any part of a nerve- 
cell-unit, although its axis cylinder process may be three 
feet in length, the effect of the stimulus is to start a 
nerve-impulse which travels upwards and downwards 
throughout the whole unit. 
(2.) That the transfer of a nerve impulse from one nerve-cell- 
unit to another can take place in one direction only. 
Supposing A and B represent two nerve-cell-units, a 
stimulus applied to A arouses a nerve-impulse which 
spreads throughout A, and occasions a nerve-impulse 
which spreads throughout B. If, however, the stimulus 
be applied to B, the nerve impulse originated is incapable 
of causing a nerve impulsein A. | 
(3.) The rate at which a nerve-impulse travels along a nerve 
was measured in 1850 by Helmholtz, and is a little over 
a mile a minute, or rather faster than an express train, 
Granted the fundamental physiological facts abovementioned and 
the anatomical knowledge of the relation of nerve-units to one 
another, one might expect to be able to predict what the path 
travelled by a nerve-impulse started in any particular area shall 
be, and hence what muscular response shall eventuate. 
In the case of some simpler reflex phenomena of the spinal 
cord we can indeed in a general way predict what result shall 
follow stimulation of a sensory nerve in a particular area. Even 
in such a case, however, the nerve impulse has to leave the nerve- 
unit in which it originated and pass to one or more other nerve- 
units, and although we may be certain that this takes place, we 
are at present unable to state how it takes place. 
Recent histological methods lead one to infer that, at any rate, 
in the dead and hardened nervous tissue there exists no absolute 
continuity between the processes of one nerve-cell and another. 
Physiological continuity must exist at the time a nerve impulse 
passes from the one to another, for all observations show how 
essential continuity of an irritable tissue is for conduction. 
Again, although one may roughly predict the direction in 
which a stimulus applied to a sensory nerve will be expressed in 
the simpler reflex actions of the spinal cord, when the reflex 
necessitates the co-operation of the more complexly arranged 
