
INAUGURAL ADDRESS. 25 
chemical stimuli enter into the protoplasm of the tissues, 
blood, nerve-centres, secreting cells, &c., and exalt, 
depress, or modify vital action by disturbing the vital- 
molecular changes; not being adapted in quantity or 
quality to renew the protoplasm as pabulum, any increased 
evolution of kinetic energy they excite must be supplied 
by wasting or consumption of protoplasm—hence fatigue, 
till the latter is renewed from fresh pabulum. As examples 
of extreme minuteness of the needful quantity among the 
forces may be noted that of mechanical force in the sense 
of tact, hearing and sight; and among the chemical 
stimuli those of taste and smell in animals; and in 
vegetables the various solutions of salts which excite the 
protoplasmic contractions of the drosera, &c. For the 
interaction of the environment in its capacity of stimulus 
is quite as essential to vegetable as to animal life, although 
not so conspicuous. This class—the stimuli—comprises 
all poisons and medicines, and material agents acting 
otherwise than as pabulum or simple conditions. 
These three divisions are set forth separately here for 
convenience, but in nature there is no such separation, 
and they are all three essential to the performance of 
every vital act. Some physiologists, however, have laid 
stress on one to the exclusion almost of the others. For 
instance, as above said, Dr. Beale puts the pabulum com- 
pletely in the foreground, and scarcely allows the existence 
of the stimuli—in fact he asserts the spontaneity of most 
vital actions. On the other hand, Fletcher, following 
John Brown, places the stimuli almost as much in the 
foreground as Beale does the pabulum, for he denies spon- 
taneity im toto, and defines life as “‘irritation,’ or the 
action of stimuli upon irritability. The word irritability 
being explained as that used by Glisson, and synonymous 
with vitality as a whole, and not restricted, as by some 
