PRESIDENT’S ADDRESS. 419 
nerve-units of the brain it is no longer possible to predict what 
will be the ultimate expression and what will be the course 
travelled by the nerve-impulse. The same stimulus apparently 
spreads one time along one path, at another in a different direction, 
It appears as if the path between one nerve-unit and another 
were not constant, but that under different sets of circumstances 
continuity were effected between different units, thereby necessi- 
tating the nerve impulse taking a varying course with varied 
result according to circumstances. 
One is so continually studying the relation of nerve-cells to one 
another in hardened and impregnated specimens, and, conse- 
quently, perhaps liable to forget that nerve-cells are alive and may 
manifest some further activities common to living things as well 
as being highly differentiated conducting tissue. The response to 
stimulus by the generation and propagation of nerve-impulse may 
not be the only outcome of their irritability, and they may be 
capable of limited movement. 
In this regafd I may mention a highly suggestive observation 
of Wiedersheim upon the cranial ganglia of a small transparent 
crustacean. As Wiedersheim examined this small creature under 
the microscope he noticed that at the time it was manifesting 
active muscular movement the ganglion cells were themselves 
motile and increased and diminished the length of some of their 
processes, much in the way of pseudopodia on a limited scale. 
This observation, if confirmed, may be the key to the under- 
standing of the continuity of nerve-units one with another. If 
the shorter processes of nerve-cells are possessed of limited move- 
ment, this movement may easily accomplish a continuity at the 
time a stimulus reaches the nerve-cell, and the differential result 
of the movement of more than one nerve-cell may be a possible 
interpretation of the variable course a nerve-impulse takes, and 
also of the hitherto unexplained phenomena of inhibition within 
the central nervous system. 
The recent progress of knowledge of the nervous system has 
been mainly anatomical, and an immense amount of work must 
assuredly be done in the same field in the future, but for a great 
advance in understanding nervous processes we must look to the 
discovery of some more fundamental physiological facts. At pre- 
sent we are mostly in the dark both as regards the nature of 
nerve-impulse, and the physiological relation of one nerve unit to 
another. Fundamental nervous phenomena must be essentially 
identical in all animals, and the observations of Wiedersheim show 
that a study of these in the lowly animals might be productive of 
fine results. 
The four instances of the kind of work physiologists have been 
doing of late years are, I think, fairly typical. From them you 
will see that a great deal of it has been minutely anatomical, and 
