158 PRESIDENT’S ADDRESS—SECTION J. 
the neurons be to the same extent. It is seen that the health of 
one set of tissues is much influenced by the normal functioning 
of other tissues with which they are physiologically closely con- 
nected. An instance may be given showing how if an area of 
the cortex be affected, deeper parts of the brain connected with it 
physiologically also suffer. If the area having to do with 
psychical visual conceptions be destroyed, it is noted that a part 
of the structure called the optic thalamus, which is intermediary 
in the visual tract between the retina of the eye and the cortex, 
begins also to show signs of degeneration. It is apparent, there- 
fore, that a part degenerates if severed from its normal in- 
fluences or not allowed to function in its usual way. As a re- 
sult of nutrition the neuron becomes increasingly capable of 
more forcible energising, and on the occurrence of an excitant 
the impulse is passed along the various processes or extensions 
which in the meantime have also been nourished. It may be 
inferentially accepted that as a result the dendritic processes 
will be developed to a fuller extent, and connections of touch 
be made wider afield. The motility of the gemmules will also 
be increased. In this way new associations become gradually 
organised and rendered capable of extended co-ordinating func- 
tioning. 
The larger extent of the sensory areas has been noted, and 
their early appearance in the course of development. From this 
may be inferred the great importance of these areas as furnish- 
ing the raw material from which psychic conceptions of a more 
associated nature will be ultimately elaborated, the site of these 
being the association areas situated between the sensory ones. 
Whilst the activity of the sphere of bodily sensibility keeps the 
organism conscious of its personality, the visual and auditory 
spheres in functioning keep it in touch with its environment. 
From what has already been said of the dependence of one part 
for its physiological activity on the proper activity of other 
parts closely connected with it anatomically, it will be evident 
that the proper health of the association areas will depend upon 
the healthy action of the sensory spheres. It is, therefore, of 
ereat imporance in efforts to educate the association areas that 
the stimuli received through the senses should reach a sufficient 
intensity to allow of a transmission of the influence into definite 
paths that may not yet be fully organised. This intensity 
of action is felt more or less by the individual as a kind of 
shock, and arouses what is called “attention.” This expressed 
physiologically, as has already been done, means that most of 
the gemmules are in a condition of retraction, and that only 
a few are functioning. The resultant sensation is consequently 
definite and intense in proportion to the limitation of general 
diffusion. In early life stimuli reaching the cortex must pro- 
duce such a shock in forming the paths along which some 
