WORKS ON THE NERVOUS SYSTEM. 
681 
Bostock, Magendie, and Mayo, have all failed in their attempts at 
explanation. Experiments have shewn, that when an instrument 
is introduced upon the root of the tongue and tonsils, an act of de- 
glutition ensues ; that the finger passed into the pharynx of a liv- 
ing animal through a wound in the neck becomes forcibly grasped ; 
that the same happens even after decapitation ; but that no action 
takes place after the division of the pharyngeal nerves, or the re- 
moval of the medulla oblongata. M. Flourens found, that an ani- 
mal, deprived of his cerebrum, no longer ate nor drank of his ow n 
accord, although food pushed a certain way into the mouth became 
perfectly swallowed. The explanation of which is, that, brain- 
less, he could neither feel his food, nor feel any appetite or desire 
to take it ; but when the food was advanced as far as the pharynx, 
there it came within the province of the excito-motory nerves, 
to the excitors of which it imparted the necessary excitation, 
and by the motors of which, through the medium of the medulla 
oblongata, the muscular parts of the pharynx and oesophagus 
were putin action, and the bolus transmitted in the usual man- 
ner into the stomach : so that, in truth, of the several acts of 
deglutition, only the acts of taking food and masticating it are 
voluntary or recognisable : the act of swallowing, although one 
that is at the beginning felt, because it is commenced by vo- 
luntary effort, goes on afterwards independently of the will ; is, 
in short., purely an excito-motory act. Supposing, therefore, 
that we are treating any case in which the voluntary power — 
the power either to take food or to masticate it — is destroyed, we 
shall find we can w 7 ell support life by the introduction of balls 
of proper aliment — as we would balls of medicine — into the 
pharynx. 
There can be no doubt, therefore, that, as far as the pharynx 
is concerned, swallowing constitutes a reflex function, requiring 
entirety of the medulla oblongata, and the actual contact of 
some substance as a stimulus; but, in regard to the completion 
of the act, although the contraction of the oesophagus takes place 
independently of volition, there exists some doubt whether it be 
a reflex action, or one partly attributable to irritability. What 
chiefly creates this diversity of opinion, is the difference of 
result obtained from the division of the par vagum. MM. Leuret 
and Lassaigne report that a horse, after the removal of five inches 
from each pneumogastric nerve, ate seven pints of oats; half of 
which, eight hours afterwards, were found in the stomach, half in 
the duodenum. In the dog, after the division of these nerves, 
deglutition was perfectly performed. But in the rabbit, accord- 
ing to Sir A. Cooper, Drs. J. Reid and Marshall Hall, the food 
stagnates in the oesophagus. 
