362 Appendix 
metabolic state. This tendency of an organism toward 
the invariability of its own metabolism has become, in 
the course of its phyletic evolution, an inherent tendency 
to pass through all the transient physiological states that 
could re-establish this necessary condition within it, hence, 
a tendency to perform all movements that have nour- 
ishment for their object; yet in doing this it has never 
relinquished its original character. This results directly 
from the fact that all inclination to procure new food 
ceases as soon as the internal nutritive system of the 
animal has attained its normal state. 
Accordingly, the hydra or sea anemone does not react 
positively to food except when its metabolism is in a 
state requiring more nutriment, “unless,” says Jennings, 
“metabolism is in such a state as to require more ma- 
terial”; for instance, when the large sea anemone 
Stoichactis helianthus is not hungry, a bit of food 
placed upon its oral disk occasions the same character- 
istic “rejecting reaction” as if it were any other disturb- 
ing object. And all other organisms, the higher as well 
as the lower, behave in exactly the same fashion.? 
Schiff’s experiments of injecting nutritive substances 
into the veins of dogs are direct evidence, on the other 
hand, that the fundamental condition of hunger is the ab- 
sence of histogenetic substances in the blood, for these 
injections resulted not only in nourishing the animal but 
also in allaying its hunger. 
Moreover the fact that hunger, especially as long 
as it is only moderate, assumes in man the form of a 
special and localized sensation originating in the wall of 
the stomach and being the sole cause of the activities 
2H. S. Jennings, Behavior of Lower Organisms, pp. 202, 205, 
etc. New York, MacMillan, 1906. 
