PRESIDENT’S ADDRESS. 27 
tary muscles. Many involuntary muscles have a natural tendency to 
continuous or rhythmic contraction which is quite independent of the 
central nervous system; in this case the effect of impulses received from 
the latter is merely to increase or diminish the amount of such contrac- 
tion. An example of this double effect is observed in connection with 
the heart, which—although it can contract regularly and rhythmically 
when cut off from the nervous system and even if removed from the 
body—is normally stimulated to increased activity by impulses coming 
from the central nervous system through the sympathetic, or to 
diminished activity by others coming through the vagus. It is due to 
the readiness by which the action of the heart is influenced 
Effects of in these opposite ways by the spread of impulses generated 
emotions, ; . : ; 
during the nerve-storms which we term ‘ emotions that 
in the language of poetry, and even of every day, the word ‘ heart ’ has 
become synonymous with the emotions themselves. 
The involuntary muscle of the arteries has its action similarly 
balanced. When its contraction is increased, the size of the vessels is 
lessened and they deliver less blood; the parts they supply accordingly 
become pale in colour. On the other hand, when the contraction 1s 
diminished the vessels enlarge and deliver more blood; the parts which 
they supply become correspondingly ruddy. These changes in the 
arteries, like the effects upon the heart, may also be produced under the 
influence of emotions. ‘Thus ‘blushing’ is a purely physiological 
phenomenon due to diminished action of the muscular tissue of the 
arteries, whilst the pallor produced by fright is caused by an increased 
contraction of that tissue. Apart, however, from these conspicuous ; 
effects, there is constantly proceeding a less apparent but not less 
important balancing action between the two sets of nerve-fibres dis- 
tributed to heart and blood-vessels ; which are influenced in one direction 
or another by every sensation which we experience and even by impres- 
sions of which we may be wholly unconscious, such as those which 
occur during sleep or anesthesia, or which affect our otherwise insénsi- 
tive internal organs. 
A further instance of nerve-regulation is seen in secreting glands. 
Not all glands are thus regulated, at least not directly; but in those 
which are, the effects are striking. Their regulation is of 
Regulation of the same general nature as that exercised upon involuntary 
igaapaen by muscle, but it influences the chemical activities of the 
e nervous 
system. gland-cells and the outpouring of secretion from them. By 
means of this regulation a secretion can be produced or 
arrested, increased or diminished. As with muscle, a suitable balance 
is in this way maintained, and the activity of the glands is adapted to 
the requirements of the organism. Most of the digestive glands are 
