26 LIVERPOOL BIOLOGICAL SOCIETY. 
recent physiologists, to the faculty of evolving actual 
energy—on the application of a stimulus—a faculty, one 
would think, equally within the power of a non-living 
machine. Others again vaguely and indiscriminately speak 
of the whole relations of the environment as conditions. 
These discrepancies may be partly accounted for by the 
fact, as above said, that all functions of the environment 
must be in operation in every vital, and also that many of 
the agents of which the environment is composed must 
act more or less in two or in all three of these capacities. 
Heat, for example, besides being always an _ essential 
condition acts as a stimulus when in excess, hurrying on 
vital action till exhaustion and death take place. Oxygen, 
which may be termed pabulum of force, because it 
furnishes potential energy in quantitative relation to the 
kinetic energy evolved in the bodily functions, is also a 
stimulus which in excess hurries on vital action to disease 
and death. Material pabulum itself is a stimulus. We 
may thus go through the greater part of the elements of 
the environment and show that stimuli are essential 
externally or internally as regards a complicated organism, 
though always externally as regards the protoplasm. We 
thus learn to be cautious in attributing spontaneity to any 
living action, but rather to appreciate the scientific reserve 
of those physiologists who speak of protoplasmic move- 
ments or functions of which the immediate exciting cause 
is not obvious, as due to stimuli or agencies as yet 
unknown, rather than conclude at once that they are 
spontaneous. 
We have now reached a point where we can give a 
complete definition of life in the abstract, viz., as ‘‘ the 
consumption and regeneration of protoplasm in co-opera- 
tion with external conditions, pabulum and stimuli.”’ Or 

