340 ANIMAL PHYSIOLOGY. 
the pharynx alone. Some persons seem to have acquired the 
power of regurgitating food and masticating it afresh. 
The excessive vomiting following obstruction of the bowels 
is comparable to the unusual action of the heart, ureter, blad- 
der, etc., when there is hindrance to the outflow. As we have 
already explained for the heart, we regard this as the resump- 
tion of a power of independent action seen'in ancestral forms 
and marked when the nervous system is no longer exercising 
its usual control and direction. Not that this or similar be- 
havior may not result from excessive stimulation, leading to 
unusual central nervous discharge, but it certainly does happen 
independently of the nervous system, and may be witnessed in 
the hearts of cold-blooded animals when all their nerves are 
divided. 
Similarly, the habit of regurgitating the food is intelligible 
in the light of evolution. The fact.that mammals are descended 
from lower forms in which unstriped muscle-cells go to form 
organs that have a rhythmically contractile function, renders 
it clear why this function may become, as in ruminants, spe- 
cialized in certain parts of the digestive tract; why carnivora 
should vomit readily, and why human subjects should learn to 
regurgitate food. There is, so to speak, a latent inherited ca- 
pacity which may be developed into actual function. Apart 
from this it is difficult to understand such cases at all. 
The vomiting center is usually located in the medulla, and 
is represented as working in concert with the respiratory center. 
But when we consider that there is usually an increased flow 
of saliva and other phenomena involving additional central 
nervous influence, we see reason to believe in co-ordinated 
action implying the use of parts of the central nervous system 
not so closely connected anatomically as the respiratory and 
vomiting centers are assumed to be. 
Indeed, as we before indicated, it does not seem probable 
that the doctrine of centers in its present form, especially with 
such precise limitations, both anatomically and physiologically, 
will continue to be maintained. We seem to have been over- 
looking the connection of parts while occupied with defining 
their limits. It is not, however, yet possible to substitute 
other explanations that shall be wholly satisfactory; and we 
make these remarks to keep the student expectant of progress, 
for, as a distinguished exponent of science has said, “ When 
Science adopts a [rigid] creed, she commits suicide.” 
We do not know the part taken, if any, by the splanchnic 
